A student investigates the resistance of a filament lamp. She sets up a circuit consisting of a d.c. power supply, a switch, an ammeter, a filament lamp LLL, and a long resistance wire CECECE with a sliding contact SSS that can move along the wire from point CCC to point EEE. A voltmeter is connected in parallel with the lamp LLL to measure the potential difference across it.
State how a voltmeter must be connected relative to the lamp.
When the sliding contact SSS is placed at point CCC (so no resistance wire is included in the circuit), the readings obtained are: V1=3.6 VV_1 = 3.6\text{ V}V1=3.6 V and I1=0.45 AI_1 = 0.45\text{ A}I1=0.45 A. Calculate the resistance R1R_1R1 of the lamp at this setting. Include the unit.
The sliding contact SSS is moved to the midpoint DDD of the resistance wire. The readings are now: V2=2.2 VV_2 = 2.2\text{ V}V2=2.2 V and I2=0.34 AI_2 = 0.34\text{ A}I2=0.34 A. Calculate the resistance R2R_2R2 of the lamp. Give your answer to a suitable number of significant figures (2 or 3).
The sliding contact SSS is moved to the end point EEE. The readings are now: V3=1.2 VV_3 = 1.2\text{ V}V3=1.2 V and I3=0.24 AI_3 = 0.24\text{ A}I3=0.24 A. Calculate the resistance R3R_3R3 of the lamp.
Complete the following statements based on these results: 1. As the length of the resistance wire included in the circuit is increased, the brightness of the lamp _______. 2. As the length of the resistance wire included in the circuit is increased, the resistance of the lamp _______.
Describe how a variable resistor (rheostat) should be connected in the circuit if used in place of the resistance wire CECECE.
452 exam-style questions on CIE IGCSE Physics 4.2 Electrical quantities, covering 4.2.1a Positive and negative charge, 4.2.1b Charging by friction and detecting charge, 4.2.1c Electrical conductors and insulators, 4.2.1d Electric fields and electric field patterns, 4.2.2a Electric current, charge and measuring current, 4.2.2b Conduction in metals and the direction of current, 4.2.2c Direct current and alternating current, 4.2.3a Electromotive force, 4.2.3b Potential difference and voltmeters, 4.2.4a Resistance, 4.2.4b Resistance of a metallic wire, 4.2.4c Current–voltage graphs, and 4.2.5 Electrical energy and electrical power. Each one has a worked solution and a mark scheme showing where the marks go.