A student investigates the resistance of a resistor and a lamp.
The student records VSV_{\text{S}}VS, the potential difference across the resistor R\text{R}R, and the current ISI_{\text{S}}IS, in the circuit:
VS=2.6 V V_{\text{S}} = 2.6\text{ V} VS=2.6 V IS=0.40 A I_{\text{S}} = 0.40\text{ A} IS=0.40 A(i) Calculate RSR_{\text{S}}RS, the resistance of resistor R\text{R}R, using the equation RS=VSISR_{\text{S}} = \frac{V_{\text{S}}}{I_{\text{S}}}RS=ISVS. Include the unit.
The student replaces the resistor with a lamp. She records VLV_{\text{L}}VL, the potential difference across the lamp, and the current ILI_{\text{L}}IL in the circuit:
VL=1.9 V V_{\text{L}} = 1.9\text{ V} VL=1.9 V IL=0.35 A I_{\text{L}} = 0.35\text{ A} IL=0.35 ACalculate RLR_{\text{L}}RL, the resistance of the lamp, using the equation RL=VLILR_{\text{L}} = \frac{V_{\text{L}}}{I_{\text{L}}}RL=ILVL.
Describe how the voltmeter must be connected to measure the combined potential difference VCV_{\text{C}}VC across the series combination of both the resistor and the lamp.
The student connects the resistor R\text{R}R and the lamp in series and records the combined potential difference VCV_{\text{C}}VC and the current ICI_{\text{C}}IC:
VC=4.5 V V_{\text{C}} = 4.5\text{ V} VC=4.5 V IC=0.32 A I_{\text{C}} = 0.32\text{ A} IC=0.32 ACalculate RCR_{\text{C}}RC, the combined resistance of the resistor and the lamp connected in series, using the equation RC=VCICR_{\text{C}} = \frac{V_{\text{C}}}{I_{\text{C}}}RC=ICVC.
State and explain briefly whether the results show that RS+RL=RCR_{\text{S}} + R_{\text{L}} = R_{\text{C}}RS+RL=RC within the limits of experimental accuracy (taken as 10%10\%10%).
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.