CAIE IGCSE Physics 4 Electricity and Magnetism

Covered syllabus points

4.1 Simple phenomena of magnetism 4.2.1 Electric charge 4.2.2 Electric current 4.2.3 Electromotive force and potential difference 4.2.4 Resistance 4.2.5 Electrical energy and electrical power 4.3.1 Circuit diagrams and circuit components 4.3.2 Series and parallel circuits 4.3.3 Action and use of circuit components 4.4 Electrical safety 4.5.1 Electromagnetic induction 4.5.2 The a.c. generator 4.5.3 Magnetic effect of a current 4.5.4 Force on a current-carrying conductor 4.5.5 The d.c. motor 4.5.6 The transformer

[Maximum number: 10]

(a)

Fig. 7.1 shows three bars of steel, A, B and C.

Fig. 7.1

A student is given the three pieces of steel. Two of the pieces are magnetised and one piece is unmagnetised.

Describe and explain how the student determines which piece is unmagnetised using only the three pieces of steel.

[ 4 ]

(b)

Fig. 7.2 shows a circuit diagram of a step-down transformer.

Fig. 7.2

[ 6 ]

(i)

The mains voltage supplied to the transformer is 240 V. The output power of the transformer is 45 W. The transformer is 100% efficient.

Calculate the input current to the transformer.
input current =

[ 3 ]

0.19 A
$I_{\mathrm{p}} V_{\mathrm{p}}=I_{\mathrm{s}} V_{\mathrm{s}}$ OR $\left(I_{\mathrm{p}}=\right) I_{\mathrm{s}} V_{\mathrm{s}} / V_{\mathrm{p}}$ OR $\left(I_{\mathrm{p}}=\right) 45 / 240$ OR $I_{\mathrm{p}} V_{\mathrm{p}}=45$ OR power in primary = power in secondary
$\left(I_{\mathrm{p}}=\right) 45 / 240$

(ii)

Draw a labelled diagram of a step-down transformer. On the labels, state a suitable material for each of the components.

[ 3 ]

[Maximum number: 6]

A lightning conductor protects a tall building and the people in it against damage and injury caused by lightning strikes.

The lightning conductor is a very long strip of copper that is attached to the side of the building. At the top of the building, the strip of copper is connected to a vertical metal pole and at the bottom of the building, it is buried in the ground.

Fig. 7.1

The bottom of the thundercloud is negatively charged.
As the cloud moves closer to the building, the top of the metal pole becomes charged.

(a)

State the sign of the charge at the top of the metal pole. Explain, in terms of the particles involved, how it becomes charged.

[ 2 ]

(b)

As the cloud passes over the building, a lightning strike occurs and a charge of 0.84 C flows through the lightning conductor. The charge flows for $3.5 \times 10^{-5} \mathrm{~s}$ .

[ 3 ]

(i)

Calculate the average current in the lightning conductor during this time.

[ 2 ]

( I= ) $Q \div t$ or $0.84 \div 3.5 \times 10^{-5}$ $2.4 \times 10^{4} \mathrm{~A}$

(ii)

It is suggested that the current in the lightning conductor could be measured by connecting a laboratory ammeter between the pole and the copper strip.

State one reason why this cannot be successful.

[ 1 ]

(c)

The copper strip has a large cross-sectional area.

State how increasing the cross-sectional area of the copper strip affects its resistance.

[ 1 ]

[Maximum number: 9]

A circuit contains two fixed resistors and a light-dependent resistor (LDR). Fig. 8.1 shows that the power supply is a 9.0 V battery.

Fig. 8.1

The current in the $450 \Omega$ resistor is 0.012 A .

(a)

State what is meant by electric current.

[ 1 ]

(b)

The current in the LDR is $I_{1}$ and the current in the $800 \Omega$ resistor is $I_{2}$ .

Complete the equation that relates the current in the $450 \Omega$ resistor to $I_{1}$ and $I_{2}$ .
current in the $450 \Omega$ resistor =

[ 1 ]

(current in the $450 \Omega$ resistor = )

(c)

Calculate the power dissipated in the $800 \Omega$ resistor.
power =

[ 4 ]

(d)

The brightness of the light that is incident on the LDR increases.

Explain what happens to the potential difference (p.d.) across the $450 \Omega$ resistor.
[Total: 9]

[ 3 ]

[Maximum number: 9]

The electromotive force (e.m.f.) of a battery is 7.5 V .

(a)

Define the term electromotive force.

[ 2 ]

(b)

The battery is connected in series with a variable resistor and a $30 \Omega$ resistor. The battery is made using 1.5 V cells.

[ 7 ]

(i)

Draw a circuit diagram that shows all the 1.5 V cells connected to produce an e.m.f. of 7.5 V , the variable resistor and the $30 \Omega$ resistor.

[ 3 ]

(ii)

The resistance of the variable resistor can be varied from $0 \Omega$ to a maximum resistance of $150 \Omega$ .

Using the axes in Fig. 7.1, draw a graph to show how the current in the circuit varies with the resistance of the variable resistor as it increases from $0 \Omega$ to $150 \Omega$ .

Determine and label the value of the maximum current on the y-axis.

Fig. 7.1

[ 4 ]

curve with negative gradient of decreasing magnitude from $0 \Omega$ to $150 \Omega$ AND does not reach the x-axis
curve / line with negative gradient from $0 \Omega$ to $150 \Omega$
y-axis labelled 0.25 where candidate's line meets the y-axis OR the mark on the y-axis labelled 0.25
$R=V / I \mathbf{OR}\left(I_{\text {max }}=\right) V / R$ OR 7.5 / 30

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CAIE IGCSE Physics 4 Electricity and Magnetism Topic Practice

Covered syllabus points

Question 1

Question (a)

Question (b)

Question (i)

Question (ii)

Question 2

Question (a)

Question (b)

Question (i)

Question (ii)

Question (c)

Question 3

Question (a)

Question (b)

Question (c)

Question (d)

Question 4

Question (a)

Question (b)

Question (i)

Question (ii)