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CAIE A-Level Physics 9.3 Resistance and Resistivity

Practise using V/I and V = IR, interpreting I–V curves, calculating resistivity and explaining temperature-dependent sensors and conductors.

Syllabus
2028–2030
Course
Physics 9702
Level
AS

Exam points

  • define and calculate resistance using V/I and V = IR, and test proportionality for Ohmic behaviour
  • interpret I–V characteristics of metallic conductors, diodes and filament lamps, including changing resistance
  • calculate resistance or resistivity with R = ρL/A and relate geometry and material to resistance
  • explain temperature-dependent resistance in filament lamps, LDRs and negative-temperature-coefficient thermistors

Covered syllabus points

9.3.1—Resistance9.3.2—V = IR9.3.3—The I–V characteristics of a metallic conductor at constant temperature, a9.3.4—That the resistance of a filament lamp increases9.3.5—Ohm’s law9.3.6—R = ρL / A9.3.7—The resistance of a light-dependent resistor (LDR) decreases9.3.8—The resistance of a thermistor decreases as the temperature increases (it

9.3 Resistance and resistivity question 1

[Maximum number: 4]

Question (a)

(a)

Define the ohm.

[ 1 ]

Question (b)

(b)

Wires are used to connect a battery of negligible internal resistance to a lamp, as shown in Fig. 7.1.

Fig. 7.1

Fig. 7.1

The lamp is at its normal operating temperature. Some data for the filament wire of the lamp and for the connecting wires of the circuit are shown in Fig. 7.2.

Fig. 7.2

Fig. 7.2

[ 3 ]

Question (i)

(i)

The diameter of the connecting wires is decreased. The total length of the connecting wires and the resistivity of the metal of the connecting wires remain the same.

State and explain the change, if any, that occurs to the resistance of the filament wire of the lamp.

[ 3 ]

9.3 Resistance and resistivity question 2

[Maximum number: 2]

A battery of electromotive force (e.m.f.) E and internal resistance r is connected to a variable resistor of resistance R, as shown in Fig. 6.1.

Fig. 6.1

Fig. 6.1

The current in the circuit is I and the potential difference across the variable resistor is V.

The battery stores 9.2 kJ of energy. The variable resistor is adjusted so that V=2.1 VV=2.1 \mathrm{~V}. Use Fig. 6.2 to:

calculate resistance R

R=

9.3 Resistance and resistivity question 3

[Maximum number: 4]

Question (a)

(a)

State Ohm's law.

[ 2 ]

Question (b)

(b)

The variation of current I with potential difference V for a filament lamp is shown in Fig. 5.1.

Fig. 5.1

Fig. 5.1

The resistance of the filament lamp increases with potential difference.

[ 2 ]

Question (i)

(i)

State how Fig. 5.1 shows this.

[ 1 ]

Question (ii)

(ii)

Explain why the resistance varies in this way.

[ 1 ]
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