Question
(a) Complete the following sentences.
(i) An electric current exists in a wire when are………………………………. made
to flow in the wire. [1]
(ii) The current in a wire may be measured using an instrument called
…………………………………………….. [1]
(iii) The potential difference across a wire may be measured by connecting
…………………………………………… across the wire. [1]
(b) A length of resistance wire is connected in a simple series circuit.
The current in it is 0.8 A. The potential difference across it is 9.6 V.
Calculate the resistance of the wire.
resistance =…………………………….. [4]
(c) The resistance wire in (b) is replaced by a greater length of wire from the same reel.
Without further calculation, state the effect this has on
(i) the resistance in the circuit,
………………………………………………………………………………………………………………….
(ii) the current in the new wire when there is a potential difference of 9.6 V across it, as before.
………………………………………………………………………………………………………………….[2] [Total: 9]
Answer/Explanation
Ans: (a) (i) charge(s) OR electron(s) NOT ions
(ii) (an) ammeter
(iii) (a) voltmeter
(b) (R =) V/I in any form 9.6/0.8
12 Ω OR ohm(s) OR volt/amp OR volts per amp
(c) (i) increases
(ii) decreases OR e.c.f. from (i)
Question
Fig. 8.1 shows a cell.
(a) What does the 1.5 V indicate about the cell?
…………………………………………………………………………………………………………………….. [2]
(b) Three cells identical to the cell in Fig. 8.1 make up a 4.5 V battery. The battery is
connected in series with a 180 Ω resistor.
Calculate the current in the circuit.
current =…………………………………………. [4]
(c) A second 180 Ω resistor is connected in parallel with the 180 Ω resistor from (b).
(i) In the space below, draw the circuit diagram of the two resistors in parallel,
connected to the battery. Use standard symbols. [3]
(ii) State the value of
1. the potential difference across the second 180 Ω resistor, ……………………………..
2. the current in the second 180 Ω resistor. ……………………………………………………..[2] [Total: 11]
Answer/Explanation
Ans: (a) its voltage/potential difference condone volts its e.m.f./electromotive force
(b) V = IR in any form OR V / R
4.5 / 180 0.025 OR 2.5 × 10–2 OR 1 / 40 A/amps/amp/a
(c) (i) two resistors shown in parallel (accept any symbol here)
condone faint lines through resistors (where attempted to rub out wire) battery in series with resistances (allow any recognisable symbol here) (even if resistances not in parallel) all symbols correct (allow cell symbol for battery) (allow rheostat for resistor condone old symbol)
(ii) 1. 4.5 (V) ignore units 2. 0.025 OR his (b) ignore units