A student is investigating the potential differences across circuit components.
First, the student connects three lamps, X\text{X}X, Y\text{Y}Y, and Z\text{Z}Z. Lamps X\text{X}X and Y\text{Y}Y are connected in series with each other, and lamp Z\text{Z}Z is connected in parallel with the series combination of X\text{X}X and Y\text{Y}Y.
The student records the total current ItotalI_{\text{total}}Itotal entering the parallel network, the potential difference VXV_{\text{X}}VX across lamp X\text{X}X, and the potential difference VYV_{\text{Y}}VY across lamp Y\text{Y}Y:
Itotal=0.45 A I_{\text{total}} = 0.45\text{ A} Itotal=0.45 A VX=1.2 V V_{\text{X}} = 1.2\text{ V} VX=1.2 V VY=1.5 V V_{\text{Y}} = 1.5\text{ V} VY=1.5 VCalculate the potential difference VseriesV_{\text{series}}Vseries across the series pair of lamps X\text{X}X and Y\text{Y}Y using the equation:
Vseries=VX+VY V_{\text{series}} = V_{\text{X}} + V_{\text{Y}} Vseries=VX+VYCalculate RtotalR_{\text{total}}Rtotal, the combined resistance of the lamps, using the equation:
Rtotal=VseriesItotal R_{\text{total}} = \frac{V_{\text{series}}}{I_{\text{total}}} Rtotal=ItotalVseriesState the unit.
The student rearranges the circuit so that the three lamps are connected in series with each other. They record the potential difference across each lamp in turn:
VX=0.8 V V_{\text{X}} = 0.8\text{ V} VX=0.8 V VY=1.1 V V_{\text{Y}} = 1.1\text{ V} VY=1.1 V VZ=0.9 V V_{\text{Z}} = 0.9\text{ V} VZ=0.9 VCalculate the total potential difference VnewV_{\text{new}}Vnew across the three series lamps using the equation:
Vnew=VX+VY+VZ V_{\text{new}} = V_{\text{X}} + V_{\text{Y}} + V_{\text{Z}} Vnew=VX+VY+VZAnother student suggests that VseriesV_{\text{series}}Vseries should be equal to VnewV_{\text{new}}Vnew. State whether the results support this suggestion and justify your answer by comparing the calculated values.
136 exam-style questions on CIE IGCSE Physics 4.3 Electric circuits, covering 4.3.1a Circuit diagrams and circuit components, 4.3.2a Series circuits, 4.3.2b Parallel circuits, 4.3.2c Current and potential difference in circuits, 4.3.2d Combined resistance of resistors in parallel, and 4.3.3 Action and use of circuit components. Each one has a worked solution and a mark scheme showing where the marks go.