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CAIE A-Level Physics 9.2 Potential Difference and Power

Practise relating potential difference to energy per charge with V = W/Q, choosing power formulae and comparing circuit energy transfer.

Syllabus
2028–2030
Course
Physics 9702
Level
AS

Exam points

  • define and calculate potential difference as energy transferred per unit charge using V = W/Q
  • calculate electrical power with P = VI, P = I²R or P = V²/R and choose the appropriate form
  • compare energy and power transfer in components using voltage, current, resistance and time

Covered syllabus points

9.2.1—The potential difference across a component as the energy transferred per9.2.2—V = W / Q9.2.3—P = VI, P = I 2R and P = V 2 / R

9.2 Potential difference and power question 1

[Maximum number: 3]

Question (a)

(a)

Define electric potential difference (p.d.).

[ 1 ]

Question (b)

(b)

An ammeter is used in the circuit in (c) to measure the current I as resistance R is varied. Fig. 6.2 is a graph of R against 1I\frac{1}{I}.

Fig. 6.2

Fig. 6.2

[ 2 ]

Question (i)

(i)

Use Fig. 6.2 to determine the power dissipated in the variable resistor when there is a current of 2.0 A in the circuit.
power = W

[ 2 ]

9.2 Potential difference and power question 2

[Maximum number: 1]

Two vertical metal plates are separated by a distance d in a vacuum, as shown in Fig. 7.1.

Fig. 7.1 (not to scale)

Fig. 7.1 (not to scale)

The potential difference (p.d.) between the plates is V. A nucleus with charge +q is initially at rest on plate X . The nucleus is accelerated by the uniform electric field from plate X along a horizontal path to plate Y .

State expressions, in terms of some or all of d, q and V, for:

the kinetic energy of the nucleus when it reaches plate Y .
kinetic energy =

9.2 Potential difference and power question 3

[Maximum number: 2]

Fig. 5.2 shows a circuit with a battery of electromotive force (e.m.f.) 12.0 V connected to a linear potentiometer AB and two identical filament lamps P and Q .

Fig. 5.2

Fig. 5.2

The battery has negligible internal resistance and the lamps each have the same I-V characteristic shown in Fig. 5.1.

When the slider of the potentiometer is at its midpoint, as shown in Fig. 5.2, the current I in the battery is 1.78 A .

Determine:

the total power dissipated in lamps P and Q
total power = W

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