Battery symbol

Pick an answer to see the reason.

1. Question 1

   This cell has been turned round and its labels hidden. Which line is its positive terminal?

   Two horizontal lines, one above the other: the lower line is long and thin, the upper line short and thick. A lead goes up from the upper line and down from the lower one.

   Whichever line is now at the top The shorter, thicker line The longer, thinner line Answer

   Not this one Right Answer

   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.

2. Question 2

   What does this drawing stand for?

   Two pairs of vertical lines in a row, each pair a long thin line and a short thick line, with a lead out to the left and a lead out to the right.

   One cell, drawn larger A battery of several cells Answer Several capacitors in a row

   Not this one Right Answer

   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.

3. Question 3

   Which source does this circle stand for?

   12

   A circle with a single sine wave inside and a lead out to each side, labelled 1 on the left and 2 on the right.

   An AC voltage source Answer A DC voltage source A current source

   Not this one Right Answer

   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.

4. Question 4

   What does the arrow inside this source circle tell you?

   12

   A circle with an arrow inside pointing from left to right, and a lead out to each side, labelled 1 on the left and 2 on the right.

   That the source can be adjusted Which terminal is at the higher voltage The direction of the current through the source Answer

   Not this one Right Answer

   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.

5. Question 5

   The labels on this source are hidden. Which terminal is at the higher potential?

   A circle with a lead out to each side. Inside the circle, a plus sign sits toward the right-hand lead and a minus sign toward the left-hand lead.

   The one drawn on the left The one beside the + sign Answer Neither: its polarity keeps alternating

   Not this one Right Answer

   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.