A student is investigating the resistance of two resistance wires, XYXYXY and WZWZWZ, using a circuit similar to the layout of a standard wire resistance experiment. Wires XYXYXY and WZWZWZ are connected together at their left ends, XXX and WWW.
The student first records the potential difference VVV and current III for a length l=0.250 ml = 0.250\text{ m}l=0.250 m of wire XYXYXY:
V=1.05 V,I=0.35 A V = 1.05\text{ V}, \quad I = 0.35\text{ A} V=1.05 V,I=0.35 AThe student repeats the measurement for l=0.500 ml = 0.500\text{ m}l=0.500 m:
V=2.03 V,I=0.34 A V = 2.03\text{ V}, \quad I = 0.34\text{ A} V=2.03 V,I=0.34 AThe student notes the readings when the sliding contact is placed on wire XYXYXY at l=0.600 ml = 0.600\text{ m}l=0.600 m with no connection between YYY and ZZZ:
V1=2.30 V,I1=0.32 A V_1 = 2.30\text{ V}, \quad I_1 = 0.32\text{ A} V1=2.30 V,I1=0.32 AThe student then connects points YYY and ZZZ with a short wire, keeping the contact at l=0.600 ml = 0.600\text{ m}l=0.600 m:
V2=2.09 V,I2=0.58 A V_2 = 2.09\text{ V}, \quad I_2 = 0.58\text{ A} V2=2.09 V,I2=0.58 ASuggest two reasons why different students all carrying out this experiment carefully, with the same apparatus, may not obtain identical results.
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.