Practice reading symbols

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The answer is “One resistor, drawn in two styles”. Three IEC symbols are rectangles: a plain rectangle is a resistor, a rectangle with a line running through it end to end is a fuse, and a rectangle joined by a dashed line to a contact is a relay coil.An inductor is drawn as a coil, a row of loops or humps for its turns. A resistor has no turns: it is a zigzag in US drawings and a plain rectangle in IEC drawings. A resistor symbol stands for a component that opposes current. The zigzag (US style) and the plain rectangle (IEC style) are two drawings of the same component.

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The answer is “The bottom end: it is the end opposite the bar”. The diode's triangle points the way conventional current flows through it during forward conduction, from anode to cathode. The triangle does not say whether the diode is conducting: that depends on the anode's potential relative to the cathode.The cathode (K) is the terminal at the bar. During forward conduction, conventional current leaves the diode at the cathode.Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing. The anode (A) is the terminal opposite the bar. During forward conduction, conventional current enters the diode at the anode.

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The answer is “Yes: wires that meet in a T are connected”. In the drawing convention used here, a dot marks a wire connection and a plain four-way crossing without a dot is not connected. Older drawings may use another convention, so check their legend. Wires that meet in a T are connected whether or not a dot is drawn there. Where four wires cross and connect, the dot is what shows it.

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The answer is “Normally closed: joined to COM while the coil is de-energised”. NC has two unrelated meanings. At a switch or relay contact it means normally closed; on an integrated-circuit pin diagram, nc marks a pin that is not connected.For the non-latching relay shown here, normal means the coil is de-energised. NO contacts are drawn open and NC contacts closed; these labels describe their resting positions. NC is the normally-closed contact: it is connected to COM in the resting, de-energised state of the single-stable relay shown here.

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The answer is “No: chassis and signal reference have marks of their own”. This sheet distinguishes earth, chassis and signal reference. They can be connected in a circuit, but the three labels have different meanings; ground does not always mean a connection to earth.The signal-reference symbol marks the chosen zero-volt reference for circuit voltages. It need not be connected to earth or chassis. The three reference marks differ in shape: earth is three horizontal lines getting shorter, chassis is a line with slanted strokes below it, and the signal reference is an open triangle pointing down.

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The answer is “IEC style”. US style names the American drawing convention used here, including the resistor zigzag. IEEE 315-1975 (ANSI Y32.2) is a historical reference; IEEE lists it as inactive-reserved, with inactivation dated 7 November 2019.Three IEC symbols are rectangles: a plain rectangle is a resistor, a rectangle with a line running through it end to end is a fuse, and a rectangle joined by a dashed line to a contact is a relay coil. A resistor symbol stands for a component that opposes current. The zigzag (US style) and the plain rectangle (IEC style) are two drawings of the same component.

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The answer is “A variable resistor”. An arrow drawn right through a resistor body marks a variable resistor with two terminals. An arrow that stops on the body is a wiper, the movable third terminal of a potentiometer.The textbooks cited here mark a thermistor in two ways: a line through the body that ends in a short flat foot rather than an arrowhead, or the letters t° beside the body. Either marks a resistance that changes with temperature; neither says whether it is NTC or PTC. A diagonal arrow through the resistor body marks a variable resistor.

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The answer is “Neither: a fixed resistor has no polarity”. This symbol has two terminals and no polarity mark. The labels 1 and 2 only tell the two ends apart.Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing. A fixed resistor has two interchangeable terminals; the symbol has no polarity.

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The answer is “A potentiometer”. A rheostat uses only two terminals, one end of the track and the wiper, where a potentiometer brings out all three: both track ends and the wiper.An arrow drawn right through a resistor body marks a variable resistor with two terminals. An arrow that stops on the body is a wiper, the movable third terminal of a potentiometer.Two arrows arriving at a resistor body mark a light-dependent resistor (photoresistor). A potentiometer has three terminals: the two ends of the resistive track and a wiper, drawn as an arrow touching the body.

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The answer is “You cannot tell from the symbol alone”. The textbooks cited here mark a thermistor in two ways: a line through the body that ends in a short flat foot rather than an arrowhead, or the letters t° beside the body. Either marks a resistance that changes with temperature; neither says whether it is NTC or PTC.The textbooks cited here mark a thermistor in two ways: a line through the body that ends in a short flat foot rather than an arrowhead, or the letters t° beside the body. Either marks a resistance that changes with temperature; neither says whether it is NTC or PTC. A thermistor's resistance changes with temperature. NTC resistance falls as temperature rises; PTC resistance rises. A generic thermistor symbol without a type label does not distinguish the two.

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The answer is “A capacitor”. In a cell symbol the long thin line is the positive terminal and the short thick line is the negative terminal.In the polarised capacitor drawings here, + marks the positive terminal. The US form has a curved negative plate; the IEC form has a hollow positive plate. The marked polarity must be respected. A cell and a capacitor are both drawn as two parallel lines. In a cell, and in each cell of a battery, the lines differ in length and the long line is the positive terminal; a capacitor's two plates are drawn the same length, and only a polarised capacitor adds a polarity mark.

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The answer is “Its capacitance can be adjusted”. A non-polarised capacitor has two interchangeable terminals.A cell and a capacitor are both drawn as two parallel lines. In a cell, and in each cell of a battery, the lines differ in length and the long line is the positive terminal; a capacitor's two plates are drawn the same length, and only a polarised capacitor adds a polarity mark. In the variable-capacitor convention used here, a diagonal arrow through the plates indicates adjustable capacitance.

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The answer is “Yes: the curved plate and the + mark it”. The − terminal is the other side of the marked polarity. In the US form here it connects to the curved plate; in the IEC form, to the plate opposite the hollow one.Most electrolytic capacitors are polarised: voltage of the wrong polarity can damage their very thin oxide insulating layer, so they are marked to show their polarity. The two words are not interchangeable, since non-polarised electrolytic capacitors also exist and are usually marked NP. In the polarised capacitor drawings here, + marks the positive terminal. The US form has a curved negative plate; the IEC form has a hollow positive plate. The marked polarity must be respected.

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The answer is “No: read the marking on the part itself”. A schematic symbol shows how terminals connect, not where they are on a real part. Terminal letters such as E, B and C or A and K do not give lead order or package layout; the part's own documentation does.Many electrolytic capacitors are marked for polarity on the part itself, typically with a − sign beside the negative lead, often printed on a stripe down the can. That marking belongs to the part, not the schematic, and it is not uniform: some parts mark the positive terminal instead, and a stripe on a non-polarised film capacitor means something else. A capacitor's + mark identifies its positive electrical terminal. A schematic does not specify physical lead length or package pinout; those require the component's own markings and documentation.

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The answer is “The positive plate”. The − terminal is the other side of the marked polarity. In the US form here it connects to the curved plate; in the IEC form, to the plate opposite the hollow one.In the variable-capacitor convention used here, a diagonal arrow through the plates indicates adjustable capacitance. The + terminal is the one the polarity mark names as positive. In the US form here it connects to the straight plate; in the IEC form, to the hollow plate.

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The answer is “The bar end”. A schematic symbol shows how terminals connect, not where they are on a real part. Terminal letters such as E, B and C or A and K do not give lead order or package layout; the part's own documentation does.Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing.The anode (A) is the terminal opposite the bar. During forward conduction, conventional current enters the diode at the anode. The cathode (K) is the terminal at the bar. During forward conduction, conventional current leaves the diode at the cathode.

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The answer is “Forward biased: the anode is more positive than the cathode”. The cathode is a terminal name, not a permanently negative terminal. During forward conduction conventional current leaves it. A cathode can be at +5 V while the anode is more positive.A diode is forward biased when its anode potential is higher than its cathode potential, and reverse biased when the cathode is higher. Page orientation does not decide bias; the current also depends on the model and connected circuit. The applied anode-side potential is higher: this is a forward-bias comparison. The ideal model permits anode-to-cathode current in the stated current-limited test; the applied values are not loaded diode voltages.

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The answer is “The anode's voltage compared with the cathode's”. The diode's triangle points the way conventional current flows through it during forward conduction, from anode to cathode. The triangle does not say whether the diode is conducting: that depends on the anode's potential relative to the cathode.Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing. A diode is forward biased when its anode potential is higher than its cathode potential, and reverse biased when the cathode is higher. Page orientation does not decide bias; the current also depends on the model and connected circuit.

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The answer is “A light-emitting diode (LED)”. An LED and a photodiode differ only in the direction of their two arrows: an LED's point away from the body, for light given out, and a photodiode's point toward it, for light received.Every diode variant here keeps the triangle and bar and adds one mark: arrows leaving the body for an LED, arrows arriving for a photodiode, bent bar ends for a Zener and hooked bar ends for a Schottky. With no added mark it is a generic diode.Zener and Schottky symbols differ only at the cathode bar: a Zener bar has bent ends and a Schottky bar has hooked ends. Two arrows leaving the diode body mark a light-emitting diode.

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The answer is “Reverse biased, so it blocks”. A diode is forward biased when its anode potential is higher than its cathode potential, and reverse biased when the cathode is higher. Page orientation does not decide bias; the current also depends on the model and connected circuit.The diode's triangle points the way conventional current flows through it during forward conduction, from anode to cathode. The triangle does not say whether the diode is conducting: that depends on the anode's potential relative to the cathode. The applied anode-side potential is lower: this is a reverse-bias comparison. The ideal diode model blocks reverse current.

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The answer is “The lead on the left”. The base is the terminal drawn against the flat bar; a small base current controls the device.The collector is the branch connected to the base bar that has no emitter arrow. The base has its own separate lead to that bar. The arrow is always on the emitter. It points out of the transistor for NPN and into it for PNP, whichever way the symbol is rotated.

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The answer is “A PNP bipolar transistor”. The arrow is always on the emitter. It points out of the transistor for NPN and into it for PNP, whichever way the symbol is rotated.A MOSFET's gate is drawn beside the channel with a gap between them, and its arrow sits on the body. A bipolar transistor's base lead meets its bar directly, and its arrow sits on the angled emitter lead. In a PNP transistor symbol the emitter arrow points in, toward the base; that inward arrow is the only mark that tells it from an NPN symbol.

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The answer is “The same transistor: the circle is optional”. In a PNP transistor symbol the emitter arrow points in, toward the base; that inward arrow is the only mark that tells it from an NPN symbol.A MOSFET's gate is drawn beside the channel with a gap between them, and its arrow sits on the body. A bipolar transistor's base lead meets its bar directly, and its arrow sits on the angled emitter lead. The enclosing circle may be omitted from a transistor symbol. With the same internal marks and terminal connections, either drawing represents the same transistor.

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The answer is “Conducting: the transistor is on”. The emitter arrow points the way conventional current flows through the emitter when the transistor conducts: out of an NPN transistor and into a PNP. Base and collector currents combine to match the arrow's direction.Under the BJT switch model, suitable circuit bias and sufficient base drive put the transistor in saturation; no base drive gives cutoff. The cases omit leakage, transition time and the active amplification region. Under the BJT switch model, sufficient base drive for the connected load gives saturation: the collector–emitter path conducts.

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The answer is “The lead on the right”. The source (S) is the channel terminal joined to the body in the three-terminal form shown here, so the controlling gate voltage is applied between gate and source.The drain (D) is the other channel terminal: the channel runs between drain and source. The gate is the insulated terminal drawn parallel to the channel with a gap between them.

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The answer is “Only the drawing style: it is still an inductor”. A transformer has two or more windings drawn facing each other, with core lines between them when it has a magnetic core. An inductor is a single winding with two terminals.In the coil convention used here, solid parallel core lines indicate iron and dashed core lines ferrite. The unmarked coil is used for air core. These drawings do not identify every material detail. Looped and semicircular coil drawings are alternative inductor forms. This sheet uses loops in its US view and humps in its IEC view; the winding and terminal roles are unchanged.

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The answer is “No: a zigzag has no turns, so it is a resistor”. A resistor symbol stands for a component that opposes current. The zigzag (US style) and the plain rectangle (IEC style) are two drawings of the same component.Looped and semicircular coil drawings are alternative inductor forms. This sheet uses loops in its US view and humps in its IEC view; the winding and terminal roles are unchanged. An inductor is drawn as a coil, a row of loops or humps for its turns. A resistor has no turns: it is a zigzag in US drawings and a plain rectangle in IEC drawings.

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The answer is “The coil's core”. A transformer has two or more windings drawn facing each other, with core lines between them when it has a magnetic core. An inductor is a single winding with two terminals.A capacitor symbol stands for two conductors separated by an insulator; the two parallel plates are a picture of that. In the coil convention used here, solid parallel core lines indicate iron and dashed core lines ferrite. The unmarked coil is used for air core. These drawings do not identify every material detail.

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The answer is “A relay”. A looped coil on its own can be an inductor, a solenoid or a relay coil, so what is drawn with it decides: a relay coil is joined to its contacts by a dashed link, and parallel lines beside a coil mark a magnetic core.A transformer has two or more windings drawn facing each other, with core lines between them when it has a magnetic core. An inductor is a single winding with two terminals. A relay symbol combines a coil with the contacts it moves, joined by a dashed mechanical link. US drawings show the coil as loops and IEC drawings as a rectangle; a plain switch has no coil.

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The answer is “A transformer”. The separate-winding transformer shown here transfers energy magnetically between windings without an internal conducting connection between them. This description excludes an autotransformer, whose windings share a conducting connection.In the coil convention used here, solid parallel core lines indicate iron and dashed core lines ferrite. The unmarked coil is used for air core. These drawings do not identify every material detail. A transformer has two or more windings drawn facing each other, with core lines between them when it has a magnetic core. An inductor is a single winding with two terminals.

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The answer is “No: the windings are linked magnetically, not by a wire”. In the transformer drawings here, parallel lines between windings indicate a magnetic core, drawn as iron-core examples. The air-core example omits these lines; another drawing's legend may use a plain coil more generally.An autotransformer is drawn as a single winding with taps rather than separate windings. Its primary and secondary connections share that winding, so there is no electrical isolation between them. The separate-winding transformer shown here transfers energy magnetically between windings without an internal conducting connection between them. This description excludes an autotransformer, whose windings share a conducting connection.

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The answer is “It is the winding the source drives”. Transformer dots mark corresponding voltage polarity: each dotted terminal has the same instantaneous polarity relative to its own winding's undotted terminal. The dots do not indicate equal voltage or current direction.Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing. The primary winding is the one driven by the source.

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The answer is “Ends with the same polarity at the same instant”. In the drawing convention used here, a dot marks a wire connection and a plain four-way crossing without a dot is not connected. Older drawings may use another convention, so check their legend. Transformer dots mark corresponding voltage polarity: each dotted terminal has the same instantaneous polarity relative to its own winding's undotted terminal. The dots do not indicate equal voltage or current direction.

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The answer is “A centre tap”. This sheet distinguishes earth, chassis and signal reference. They can be connected in a circuit, but the three labels have different meanings; ground does not always mean a connection to earth.An extra lead joined partway along a coil marks a tapped inductor: the tap is a connection to part of the winding. A centre tap is an electrical connection at the midpoint of a winding, shown as an extra lead from that winding.

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The answer is “An air core: there is no magnetic core”. A transformer has two or more windings drawn facing each other, with core lines between them when it has a magnetic core. An inductor is a single winding with two terminals.The separate-winding transformer shown here transfers energy magnetically between windings without an internal conducting connection between them. This description excludes an autotransformer, whose windings share a conducting connection. In the transformer drawings here, parallel lines between windings indicate a magnetic core, drawn as iron-core examples. The air-core example omits these lines; another drawing's legend may use a plain coil more generally.

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The answer is “DPDT”. Count the arms and look for a coil: an SPDT switch has one arm between two fixed contacts, a DPDT switch has two arms tied by a dashed link, and a relay adds a coil linked to its contacts.A double-pole, single-throw (DPST) switch has two moving poles worked by one mechanism, each closing onto its own fixed contact. It acts like two SPST switches linked together.A dashed line joining parts of a symbol shows a mechanical link: the parts move together, but the line is not a wire and carries no current. A double-pole, double-throw (DPDT) switch works like two SPDT switches ganged together. The dashed line between its two arms is a mechanical link: the arms move together, but no current passes along it.

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The answer is “One: the contact the arm closes onto”. Poles count the separate circuits a switch controls; throws count the contact destinations available to each pole. An off position is not an additional throw.Poles count the separate circuits a switch controls; throws count the contact destinations available to each pole. An off position is not an additional throw. In a switch symbol the moving arm is the pole, and each fixed contact it can close onto is a throw.

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The answer is “Normally closed”. Switch contacts are drawn in their normal status: the position they rest in with no force applied. A normally-open (NO) contact is drawn open and a normally-closed (NC) contact closed; for a momentary push button, normal means not pressed.The momentary-switch model has two settled states: released, with the contacts in their drawn normal status, and pressed, with each contact in the opposite state. It leaves out contact bounce, contact resistance and latching. The two push buttons differ only in the resting position drawn: the normally-open bar is drawn clear of its contacts and the normally-closed bar touching them. Pressing reverses each one; the drawing does not change.

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The answer is “No: the arm is lifted clear”. The ideal-contact model treats an open contact as electrically isolating, so no current passes, and a closed contact as making its two terminals electrically common, with no voltage between them. It leaves out contact bounce and contact resistance.The ideal-contact model treats an open contact as electrically isolating, so no current passes, and a closed contact as making its two terminals electrically common, with no voltage between them. It leaves out contact bounce and contact resistance. Under the ideal-contact model, an open switch breaks the conducting path between its two terminals.

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The answer is “It returns to the position it is drawn in”. A momentary switch has an internal spring that returns it to its resting position as soon as it is released. A switch without that spring, such as a knife switch or most toggle switches, stays wherever it was last put.The two push buttons differ only in the resting position drawn: the normally-open bar is drawn clear of its contacts and the normally-closed bar touching them. Pressing reverses each one; the drawing does not change. The momentary push buttons shown here change contact state while pressed and return to their drawn, unactuated state when released.

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The answer is “COM and NC”. For the non-latching relay shown here, normal means the coil is de-energised. NO contacts are drawn open and NC contacts closed; these labels describe their resting positions.COM is the common contact, the one the moving arm belongs to.NC is the normally-closed contact: it is connected to COM in the resting, de-energised state of the single-stable relay shown here. Under the single-stable relay model, the coil is de-energised and settled: COM–NC is closed and COM–NO is open. This is the drawn resting state.

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The answer is “Nothing: they name the resting positions”. For the non-latching relay shown here, normal means the coil is de-energised. NO contacts are drawn open and NC contacts closed; these labels describe their resting positions.In every case the printed relay contact stays drawn in its resting, de-energised position, and the NO and NC labels stay where they are. Only the highlight shows the present position. In the single-stable changeover relay shown here, energising the coil transfers COM from NC to NO after the operating delay. The printed symbol and its NO/NC labels remain unchanged.

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The answer is “COM”. NO is the normally-open contact: it is disconnected from COM at rest and connected after the coil has energised the single-stable relay shown here.NC is the normally-closed contact: it is connected to COM in the resting, de-energised state of the single-stable relay shown here.The two coil terminals are the control side of the relay; the current that flows through them moves the contacts. COM is the common contact, the one the moving arm belongs to.

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The answer is “No current: it is a mechanical link”. A dashed line joining parts of a symbol shows a mechanical link: the parts move together, but the line is not a wire and carries no current.The electromechanical relay shown here uses a coil to move contacts. Its coil circuit is electrically separate from the switched contact circuit. The dashed line between coil and contact is the mechanical link; it carries no current.

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The answer is “30”. Automotive relays often carry numbers from the German DIN 72552 terminal scheme instead of COM, NO and NC: 85 and 86 are the coil terminals, 30 is the common contact, 87 the normally-open contact and 87a the normally-closed contact.

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The answer is “Earth”. The three reference marks differ in shape: earth is three horizontal lines getting shorter, chassis is a line with slanted strokes below it, and the signal reference is an open triangle pointing down.The chassis symbol (hatched) marks a connection to the equipment's metal frame or enclosure. In the convention used here, three horizontal lines of decreasing length identify a connection to earth. Check a drawing's legend: the same shape is sometimes used more generally for circuit ground.

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The answer is “The equipment's metal frame or enclosure”. This sheet distinguishes earth, chassis and signal reference. They can be connected in a circuit, but the three labels have different meanings; ground does not always mean a connection to earth.The three reference marks differ in shape: earth is three horizontal lines getting shorter, chassis is a line with slanted strokes below it, and the signal reference is an open triangle pointing down. The chassis symbol (hatched) marks a connection to the equipment's metal frame or enclosure.

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The answer is “No: it marks the circuit's 0 V reference”. This sheet distinguishes earth, chassis and signal reference. They can be connected in a circuit, but the three labels have different meanings; ground does not always mean a connection to earth.A label such as GND, Gnd or 0 V at a reference symbol names the node that other potentials are measured from. A drawing may keep separate commons, such as an analog signal common and a digital logic common, so differently named references must not be assumed to be joined. The signal-reference symbol marks the chosen zero-volt reference for circuit voltages. It need not be connected to earth or chassis.

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The answer is “No: references with different names are not assumed joined”. Within the drawing's stated scope, repeated supply or reference labels identify the same node without a drawn wire between them. Different labels or reference symbols must not be assumed connected.Within the drawing's stated scope, repeated supply or reference labels identify the same node without a drawn wire between them. Different labels or reference symbols must not be assumed connected. A label such as GND, Gnd or 0 V at a reference symbol names the node that other potentials are measured from. A drawing may keep separate commons, such as an analog signal common and a digital logic common, so differently named references must not be assumed to be joined.

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The answer is “One, at the end of its lead”. The three reference marks differ in shape: earth is three horizontal lines getting shorter, chassis is a line with slanted strokes below it, and the signal reference is an open triangle pointing down.A ground or reference symbol marks a connection to the circuit's common reference, not a part, so the drawings here give it no reference designator. A label such as GND or 0 V names that node instead. Each ground or reference symbol shown here has one connection point to the circuit; it identifies a reference connection, not a two-terminal component.

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The answer is “The longer, thinner line”. Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing.A cell and a capacitor are both drawn as two parallel lines. In a cell, and in each cell of a battery, the lines differ in length and the long line is the positive terminal; a capacitor's two plates are drawn the same length, and only a polarised capacitor adds a polarity mark. In a cell symbol the long thin line is the positive terminal and the short thick line is the negative terminal.

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The answer is “A battery of several cells”. A cell is one long-and-short pair of lines; a battery repeats the pair, drawn as several cells in a row. Both follow the same rule: the long line is positive.A cell and a capacitor are both drawn as two parallel lines. In a cell, and in each cell of a battery, the lines differ in length and the long line is the positive terminal; a capacitor's two plates are drawn the same length, and only a polarised capacitor adds a polarity mark. A battery is drawn as several cells in a row; the terminals follow the same long-positive rule.

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The answer is “An AC voltage source”. The three source circles are told apart by the mark inside: + and − signs for a DC voltage source, a sine wave for an AC voltage source and an arrow for a current source.The generic current-source drawing used in both views is a circle with an arrow giving conventional current direction. An ideal current source fixes that current; the arrow does not give voltage polarity. The sinusoidal AC voltage-source drawing used here is a circle with a sine wave inside.

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The answer is “The direction of the current through the source”. A diagonal arrow through a symbol marks it as adjustable, whatever the component, so the body under the arrow says what it is: plates for a variable capacitor, a zigzag or rectangle for a variable resistor, a coil for a variable inductor.Conventional current leaves the ideal current source at the arrowhead end; this does not specify that terminal's voltage polarity. The generic current-source drawing used in both views is a circle with an arrow giving conventional current direction. An ideal current source fixes that current; the arrow does not give voltage polarity.

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The answer is “The one beside the + sign”. Rotating or mirroring a whole symbol, with its terminal identities and connections preserved, does not change the component. The terminal labels move with the drawing.The sinusoidal AC voltage source shown here alternates its polarity between its two terminals; neither terminal is permanently positive. The + mark identifies the higher-potential terminal relative to the − terminal. The polarity marks alone do not determine whether current is entering or leaving the source.

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The answer is “No: the switch and the lamp sit between them”. In the ideal-wire schematic model, a node is the set of points connected by uninterrupted wire. Those points share one potential; real wire resistance and other wire effects are omitted.

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The answer is “No: without a dot they are not connected”. A small half-circle hop where one wire passes over another also means the wires are not connected. Some drawings put a hop at every unconnected crossing and a dot at every connection, so neither is left to guess. In the newer convention used here, wires that cross with no dot are not connected. Older schematics drew connected wires as a plain crossing and made unconnected wires hop over each other with a small half-circle, so check a drawing's legend.

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The answer is “A relay”. Reference designators identify parts with class letters and a number. Common letters used here are R resistor, C capacitor, D diode, Q transistor, L inductor, T transformer, S switch, K relay and F fuse; other naming systems exist.

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The answer is “Yes: stubs with the same label are one node”. Within the drawing's stated scope, repeated supply or reference labels identify the same node without a drawn wire between them. Different labels or reference symbols must not be assumed connected.A schematic describes electrical connections only, not where parts sit. Parts can be moved or redrawn anywhere on the page without changing the circuit, as long as every connection is kept. A supply connection is often drawn as a short labelled stub or dot, such as +5 V, VCC or VDD, instead of a wire back to the source. The source's other side is taken to be the ground reference, and every stub with the same label is the same node.

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The answer is “4.7 kΩ”. Values printed beside a symbol may put the multiplier letter where the decimal point would be: 4k7 means 4.7 kΩ, 3R9 means 3.9 Ω, 47R means 47 Ω and 2M2 means 2.2 MΩ. IEC 60062 sets out this letter code.