Electricity & D.C. Circuits (Topic test)

The potential difference V across a filament lamp is slowly raised from zero to its normal operating value. Which graph represents the variation with V of the current I in the lamp?

• A

• B

• C

• D

Two lamps are connected in series to a 250V power supply. One lamp is rated 240V, 60W and the other is rated 10V, 2.5W. Which statement most accurately describes what happens?

• Both lamps light at less than their normal brightness.

• Both lamps light at their normal brightness.

• Only the 240V lamp lights.

• The 10V lamp blows.

Which equation is used to define resistance?

• energy = (current)2 × resistance × time

• potential difference = current × resistance

• power = (current)2 × resistance

• resistivity = resistance × area ÷ length

The charge that a fully charged 12V car battery can supply is 100kC. The starter motor of the car requires a current of 200A for an average period of 2.0 s. The battery does not recharge because of a fault. What is the maximum number of times the starter motor of the car can be used?

• 21

• 25

• 42

• 250

A potential divider circuit is formed by connecting a battery of negligible internal resistance in series with two variable resistors, as shown.

(see image)

The variable resistors have resistances R_X and R_Y.

V_X is the potential difference across resistance R_X.

R_X and R_Y are both changed at the same time.

Which combination of changes must cause V_X to increase?

• R_X larger, R_Y larger

• R_X larger, R_Y smaller

• R_X smaller, R_Y larger

• R_X smaller, R_Y smaller

In the circuit shown, contact may be made at any point along the 3Ω resistor (potentiometer).

(see image)

The battery has e.m.f. 9V and negligible internal resistance. What is the maximum range of the output voltage?

• 0 - 2 V

• 0 - 5 V

• 2 - 3 V

• 2 - 5 V

The diagram shows a junction in a circuit where three wires P, Q and R meet. The currents in P and Q are 1A and 3A respectively, in the directions shown.

(see image)

How much charge passes a given point in wire R in a time of 5s?

• 0.4 C

• 2 C

• 10 C

• 20 C

A wire carries a current of 2.0A for 1.0 hour. How many electrons pass a point in the wire in this time?

• 1.2 × 10^–15

• 7.2 × 10³

• 1.3 × 10¹⁹

• 4.5 × 10²²

The diagram shows an electric circuit in which the resistance of the external resistor is 2R and the internal resistance of the source is R.

(see image)

What is the ratio :

(power in internal resistance) / (power in external resistor) ?

• 1/4

• 1/2

• 2

• 4

The graph shows the variation with potential difference V of the current I in components X, Y and Z.

(see image)

Which row correctly identifies the components?

• X is a metallic conductor at constant temperature; Z is a semiconductor diode; Y is a filament lamp

• Y is a metallic conductor at constant temperature; X is a semiconductor diode; Z is a filament lamp

• Y is a metallic conductor at constant temperature; Z is a semiconductor diode; X is a filament lamp

• Z is a metallic conductor at constant temperature; Y is a semiconductor diode; X is a filament lamp