Question

A student investigates how the resistance of a wire changes with length.
Fig. 9.1 shows the equipment she uses.

(a) The student moves the crocodile clips to change the length of the wire.
She measures this length with the ruler and uses the ammeter reading to calculate the resistance of the wire.
When the wire is made longer, the reading on the ammeter decreases.
Explain why the reading on the ammeter decreases.

(b) Fig. 9.2 shows a length of wire connected in series with another component labelled X.

(i) State the name of the component labelled X in Fig. 9.2.

(ii) The student uses the component labelled X to vary the potential difference across the length of wire.

The student records the potential difference across the wire and the current in the wire.
Fig. 9.3 shows her results.

Use Fig. 9.3 to determine the resistance of the wire.

                                                         resistance = ……………………………………………… Ω

(c) The student chooses to use a maximum electromotive force (e.m.f.) of 1.5V.
State the meaning of the term electromotive force (e.m.f.).
(d) On Fig. 9.4, draw the shape and direction of the magnetic field around the current‐carrying wire.

▶️Answer/Explanation

Ans : 9(a) (as length increases) resistance increases ;
(as resistance increase) current decreases / resistance inversely proportional to resistance ;

9(b)(i) variable resistor ;
9(b)(ii) (resistance = ) V / I / 1.50/ 0.80 ;
(resistance = ) 1.9 (Ω) ;

9(c) energy supplied / (electrical) work done (by a source) ;
driving charge around a (complete) circuit / per (unit) charge around a (complete) circuit ;

9(d) concentric circle(s) around wire ;
direction shown anti-clockwise ;