2.1 Current, Potential Difference and Resistance

Question 1

Describe the circuit symbol for a cell.

Answer 1

[Horizontal line that’s connected to] a vertical line with a space in between, then, there’s another vertical line but it is shorter [with a horizontal line connected to it].

Question 2

Describe the circuit symbol for a battery.

Answer 2

Two cells with a dotted line going from one shorter vertical line to the other.

Question 3

Describe the circuit symbol for a lamp.

Answer 3

An ‘X’ enclosed in a circle, touching its circumference.

Question 4

Describe the circuit symbol for a fuse.

Answer 4

A rectangle with a line [the wire] going through it.

Question 5

Describe the circuit symbol for a voltmeter.

Answer 5

A ‘V’ enclosed in a circle.

Question 6

Describe the circuit symbol for an ammeter.

Answer 6

An ‘A’ enclosed in a circle.

Question 7

Describe the circuit symbol for a diode.

Answer 7

A skip button (equilateral triangle facing left connected to a vertical line at its tip - single point) enclosed in a circle, touching its circumference.

Question 8

Describe the circuit symbol for a resistor.

Answer 8

A rectangle.

Question 9

Describe the circuit symbol for a thermistor.

Answer 9

A rectangle with ‘hockey stick’ (forward slash with horizontal line connected at the bottom of the slash and out of the rectangle) , facing South-West, going through it.

Question 10

Describe the circuit symbol for a variable resistor.

Answer 10

A rectangle with an arrow, facing North-East, going through it.

Question 11

Describe the circuit symbol for a LDR.

Answer 11

A rectangle (resistor) enclosed in a circle with two arrows facing the circle from the outside.

Question 12

Describe the circuit symbol for a LED.

Answer 12

A diode enclosed in a circle, touching its circumference, with arrows facing away from the circle from the outside.

Question 13

What is electric current?

Answer 13

The rate of flow of electrical charge.

Question 14

State the equation linking charge, current and time. Give the units for the quantities involved.

Answer 14

Q =It
Charge (Coulombs), Current (Amperes), Time (Seconds)

Question 15

What can be said about the value of current at any point in a single closed loop?

Answer 15

Current is the same at all points in a closed loop.

Question 16

What two factors does the current in a circuit depend on?

Answer 16

1. Potential Difference (V)
2. Resistance (R)

Question 17

What equation should be used to calculate potential difference if current and resistance are known? State their units.

Answer 17

V = IR
Potential Difference (V), Current (A), Resistance (Ω)

Question 18

What is an ‘Ohmic Conductor’? (2)
What conditions are required for this?

Answer 18

● A conductor for which current and potential difference are directly proportional; the resistance remains constant as the current changes.
● Temperature must be constant

Question 19

In what components is the resistance not constant as the current changes? (4)

Answer 19

1. Lamps
2. Diodes
3. Thermistors
4. Light Dependant Resistors (LDRs)

Question 20

What happens to the resistance of a filament lamp as the temperature increases? Why? (4)

Answer 20

● Resistance increases
● Ions in metal have more energy, so vibrate
more, causing more collisions with electrons as they flow through the metal, creating greater resistance to current flow