Electrical circuits P2 – part 2

Common components

What they do Variable resistor – can change the resistance in a circuit. Diode – Only allows current to flow one way (direction of the arrow) LDR – Light dependant resistor (High light is low resistance) Thermistor – Heat dependant resistor (High heat is low resistance)

D – variable resistor. D- Variable resistor.

Meters and their places Voltmeters measure potential difference and are placed in parallel. Ammeters measure current and are placed in series.

State what is measured by the meters. (2) Meter 1 measures Meter 2 measures

(ii) The meter that measures potential difference is (1) A in parallel with the power supply B in parallel with the lamp C in series with the lamp D in series with the component X

Complete the circuit below with an ammeter and a voltmeter correctly connected. The power supply, variable resistor and lamp symbols are already drawn for you. (3)

B in parallel with the lamp correct symbol for ammeter or voltmeter (seen anywhere) (1) one meter connected in parallel with lamp/variable resistor/supply and one meter in series with lamp(1) both meters correctly connected (ammeter in series and voltmeter in parallel with lamp) (1) Ignore gaps, lines through symbols and wire connected to side of variable resistor Symbols do not have to be correct for this mark voltmeter connected across both components is same as voltmeter connected across supply Symbols do not have to be correct for this mark any shape, labelled ammeter, in series with lamp AND any shape, labelled voltmeter, in parallel with lamp gains marking points 2 and 3

Graphs and formula – model an answer. Complete these points then do a line of best fit

curve of best fit judged by eye (1) Must pass through zero and two other points. 5 th point can be either (8.0,0.42) or (8.0, 0.44) straight line of best fit through origin tolerance between lines A and B shown on the diagram 5 th point can be either (8.0,0.42) or (8.0, 0.44)

(c)(i ) point correctly plotted at 2.0, 0.14 to within half a small square (1) smooth curve of best fit connecting all given points within half a small square (1) Judge curve by eye. If more than one line present then ignore any that appear to be erased or deleted. Ignore any part of line which goes beyond given points. If plotted point is incorrect then allow ecf for line (2) (c)(i i) a description including two of the following:  current increases as voltage increases (1)  current is not proportional to the pd (1)  gradient gets less (1) Allow reverse argument positive correlation (between them ) graph is not a straight line not in equal steps current does not increase as much (as it gets higher) accept resistance has increased with increase in current for two marks (2) (c)(i ii) a suggestion to include: there is still a current (when control is at min position) (1) make the battery last longer (1) to break the circuit to switch the current off accept flow of electricity/charge/electrons for current battery / energy would be drained /used up/ wasted otherwise accept reverse arguments ignore reference to power / volts (2)

A description including  resistance changed (1)  reduced/decreased/lowered (1) OR  voltage/p.d /EMF (of supply) changed (1)  increased /turned up/higher(1) remove (variable) resistor /component X (2) number of batteries/number of cells add another cell/battery/battery pack/power pack/power supply (2)

substitution (1) 10/0.44 or 250/11 evaluation (1) 23 (ohms) give full marks for correct answer, no working 22.7(ohms),22.73 (ohms), 22.72(ohms) Ignore excessive decimal places.