[Maximum number: 1]

The angular deflection of the needle of an ammeter varies with the current passing through the ammeter as shown in the graph.

Which diagram could represent the appearance of the scale on this meter?

[Maximum number: 2]

Lightning occurs when charge builds up in the atmosphere, creating a potential difference between the ground and the atmosphere.

During a lightning strike there is an average current of $3.3 \times 10^{4} \mathrm{~A}$ for a time of $2.6 \times 10^{-5} \mathrm{~s}$ .

(a)

Calculate the charge transferred during the lightning strike.
charge = C

[ 2 ]

[Maximum number: 2]

An electron in a metal rod moves randomly about a mean position. When an alternating voltage is applied to the ends of the rod, the mean position can be considered to oscillate with simple harmonic motion along the axis of the rod. Fig. 4.1 shows the variation with time t of the displacement x of the mean position from a fixed point on the axis of the rod.

Fig. 4.1

(a)

The rod has a cross-sectional area of $4.3 \mathrm{~cm}^{2}$ and contains a number density of conduction electrons (charge carriers) of $8.5 \times 10^{28} \mathrm{~m}^{-3}$ .

All of the conduction electrons in the rod may be assumed to be oscillating in phase with, and with the same amplitude as, the oscillation shown in Fig. 4.1.

[ 2 ]

(i)

Use the information in (a)(iii) to calculate the magnitude $I_{0}$ of the maximum current in the rod.

I_{0}=

[ 2 ]

[Maximum number: 2]

An electric heater is to be made from nichrome wire. Nichrome has a resistivity of $1.0 \times 10^{-6} \Omega \mathrm{~m}$ at the operating temperature of the heater.
The heater is to have a power dissipation of 60 W when the potential difference across its terminals is 12 V .

(a)

For the heater operating at its designed power,

[ 2 ]

(i)

calculate the current,
current = A

[ 2 ]

[Maximum number: 1]

A student sets up a circuit with a battery, an ammeter, a heater and a light-dependent resistor (LDR) all in series.

The battery has negligible internal resistance.
A voltmeter is connected across (in parallel with) the heater.

(a)

The heater is a wire made of metal of resistivity $1.1 \times 10^{-6} \Omega \mathrm{~m}$ . The wire has length 2.0 m and cross-sectional area $3.8 \times 10^{-7} \mathrm{~m}^{2}$ .

The reading on the voltmeter is 4.8 V .
Calculate:

[ 1 ]

(i)

the reading on the ammeter.
reading on ammeter =
A

[ 1 ]

[Maximum number: 1]

For a current-carrying wire, the current can be calculated using the equation shown.

I=A n v q

What is the meaning of n ?

the number of charge carriers in the wire

the number of charge carriers multiplied by the volume of the wire

the number of charge carriers per unit length of the wire

the number of charge carriers per unit volume of the wire

[Maximum number: 1]

The diagram shows the symbol for a wire carrying a current I.

What does this current represent?

the charge flowing past a point in the wire per unit time

the number of electrons flowing past a point in the wire per unit time

the number of positive nuclei flowing past a point in the wire per unit time

the number of protons flowing past a point in the wire per unit time

[Maximum number: 1]

The number of free electrons passing a point in a wire in 24 hours is $6.0 \times 10^{23}$ . What is the average current in the wire?

6.3 pA

$1.1 \mathrm{~A}$

67 A

4.0 kA

[Maximum number: 1]

An electric current I is given by the formula I=A n v q.
What do each of the symbols represent for an electric current in a metal wire?

area of
cross-section

number of free
electrons

voltage

charge of each
nucleus

area of
cross-section

number of free
electrons per unit
volume

average drift
speed of free
electrons

charge of each
electron

current

number of free
electrons

average drift
speed of free
electrons

charge of each
nucleus

current

number of free
electrons per unit
volume

voltage

charge of each
electron

[Maximum number: 1]

There is an electric current in a copper wire.
Which statement describing the average drift speed of the charge carriers in the wire is correct?

It is nearly $3 \times 10^{8} \mathrm{~ms}^{-1}$ .

It is proportional to the cross-sectional area of the wire.

It is proportional to the length of the wire.

It is proportional to the magnitude of the current.