Electromagnetic effects

What produces an electromotive force (e.m.f.)?

Feb/March 2016

A current flows through a coil that is placed in a magnetic field, and the coil feels a turning force. Which device makes use of this effect?

Feb/March 2016

A magnet is hung from a spring so that it may move freely within a fixed coil. The coil is linked to a sensitive centre-zero galvanometer. The magnet moves up and down slowly and repeatedly. What will the galvanometer indicate?

Feb/March 2016

What generates an electromotive force (e.m.f.)?

Feb/March 2016

An electron enters a uniform magnetic field. The arrow indicates the electron’s initial direction of motion. The magnetic field is directed into the plane of the page (away from you). In what direction does a force act on the electron as it enters the magnetic field?

Feb/March 2016

The diagram illustrates an a.c. generator. At the instant the coil moves through the position shown, the output voltage is $+10\,\text{V}$. At what point does the output voltage change to $-10\,\text{V}$?

Feb/March 2016

The diagram depicts a simple transformer with an input of $240\,\text{V}$ and an output of $40\,\text{V}$. The primary coil has 600 turns. How many turns are on the secondary coil?

Feb/March 2017

A wire is positioned between the poles of a horseshoe magnet. A current flows through the wire in the direction indicated, and this produces a force on the wire. Three further setups, P, Q and R, of the wire and magnet are arranged as shown. Which arrangements produce a force in the same direction as in the original setup?

Feb/March 2017

The diagram represents a simple transformer with an input of $240\text{ V}$ and an output of $40\text{ V}$. The primary coil has $600$ turns. How many turns does the secondary coil have?

Feb/March 2017

The diagram represents a current-carrying wire. The wire is positioned at $90^\circ$ to a magnetic field. The magnetic field points into the page. A force is produced on the wire because of the current and the magnetic field. In what direction does the force act?

Feb/March 2017

As shown in Fig. 11.1, an electrical conductor is positioned between the poles of a magnet.

Feb/March 2017

(i) Suggest the material used for the two coils. State why this material is chosen. (ii) Suggest the material used for the core. State why this material is chosen.

Feb/March 2017

The diagram illustrates how the coil, armature and contacts are set up in a relay. Which diagram shows this setup when no current flows in the coil?

Feb/March 2018

The diagram illustrates a simple rotating d.c. electric motor. Which alteration causes the motor to turn faster?

Feb/March 2018

A current in a coil creates a magnetic field around the coil, as illustrated. The potential difference across the coil is made larger and its direction is reversed. What happens to the magnetic field?

Feb/March 2018

A teacher demonstrates electromagnetic induction with the apparatus illustrated in Fig. 10.1. The labels shown are spring, magnet with poles S and N, coil and centre-zero millivoltmeter.

Feb/March 2018

State three factors that influence the magnitude of the deflection.

Feb/March 2018

A student wants to show electromagnetic induction. He has a magnet and connecting wires. What other apparatus does he require?

Feb/March 2019

A transformer is connected to a $240\,\text{V}$ a.c. supply, as shown in the diagram. What is the potential difference across the transformer’s secondary coil?

Feb/March 2019

A coil that carries current is placed in a magnetic field. What effect acts on the coil?

Feb/March 2019

A coil carrying a current is put into a magnetic field. What effect does the coil experience?

Feb/March 2019

Fig. 11.1 is a diagram of a relay.

Feb/March 2019

Explain why a very high voltage is chosen.

Feb/March 2019

The diagram illustrates a transformer with an output voltage of $12\,\text{V}$. How many turns of wire are present in the secondary coil?

Feb/March 2020

A wire carrying a current is positioned between two magnetic poles. Because of the current, a force acts on the wire. Three further setups, P, Q and R, showing the wire and the magnetic poles, are arranged as shown. Which setups produce a force in the direction opposite to that shown in the diagram?

Feb/March 2020

The diagram illustrates a transformer with an output voltage of $12\,\text{V}$. How many turns of wire are there in the secondary coil?

Feb/March 2020

The diagrams illustrate different particles travelling through a magnetic field. Which particle is acted on by a magnetic force directed upwards, out of the plane of the paper?

Feb/March 2020

Fig. 10.1 illustrates an arrangement used to make an electromagnet.

Feb/March 2020

Describe the magnetic effect of this alternating current.

Feb/March 2020

The diagram illustrates an electromagnet positioned close to a coil of wire that is connected to a voltmeter. The voltmeter reading is zero. The switch is then closed. The electromagnet becomes magnetised rapidly. What happens to the voltmeter reading?

Feb/March 2021

Which diagram shows the voltage output from a simple a.c. generator?

Feb/March 2021

The diagram shows an electromagnet placed close to a coil of wire that is connected to a voltmeter. The voltmeter reads zero. The switch is then closed. The electromagnet becomes magnetised rapidly. What happens to the voltmeter reading?

Feb/March 2021

Which graph represents the voltage output of an a.c. generator with the peaks and zeros labelled correctly?

Feb/March 2021

Fig. 8.1 illustrates the magnetic field arrangement around a bar magnet. Fig. 8.1 depicts a bar magnet with poles marked S and N, together with magnetic field lines showing arrows. Fig. 8.2 illustrates two bar magnets producing a uniform magnetic field. The labels shown are: bar magnet; separation of poles; uniform magnetic field; current-carrying wire; poles N and S.

Feb/March 2021

Fig. 7.1 illustrates a horizontal conducting wire XY positioned between two opposite magnetic poles. The wire XY makes a circuit with an ammeter.

Feb/March 2021

A wire is pulled downward at right angles to the magnetic field. Three alterations are proposed. Which of these changes would make the electromotive force (e.m.f.) induced in the wire larger?

Feb/March 2023

In an experiment, a wire is positioned above a compass needle as illustrated. An electric current is then turned on in the wire, causing the compass needle to deflect. Which row gives the explanation for this effect and also states what occurs when the current is reversed?

Feb/March 2023

As time passes, the magnets in an electric motor become weaker. Which row gives two methods for keeping the motor operating at its initial speed?

Feb/March 2023

A wire is moved downward at right angles to the magnetic field. Three possible changes are listed below. 1 The speed of the movement of the wire is increased. 2 The magnetic field strength is decreased. 3 The direction of the magnetic field is reversed. Which of these changes increase the electromotive force (e.m.f.) induced in the wire?

Feb/March 2023

A wire is moved through a magnetic field. As a result, an induced current is produced in the wire. This induced current then acts with the magnetic field, creating a force on the wire. What is the direction of this force?

Feb/March 2023

A $100\%$ efficient step-down transformer has primary voltage $V_p$ and primary current $I_p$. Which row compares the secondary voltage with $V_p$ and the secondary current with $I_p$?

Feb/March 2023

Fig. 10.1 depicts two wire coils, P and Q, each placed in its own circuit. Their ends lie close together, but they do not make contact.

Feb/March 2023

Fig. 8.1 shows a flat coil positioned horizontally inside a magnetic field. The diagram marks N, S, coil, axis, and points A and B. The coil is linked to a cell, and the coil rotates.

Feb/March 2023

Which device operates by using the magnetic effect of an electric current?

Feb/March 2024

A transformer contains 200 turns on its primary coil and is connected to a $240\,\text{V}$ a.c. supply. Its output voltage is $60\,\text{V}$ a.c. How many turns are there on the transformer’s secondary coil?

Feb/March 2024

The diagram illustrates a transformer. What output voltage is produced?

Feb/March 2024

A beta-particle enters a uniform magnetic field that points into the plane of the page and is deflected downwards, as shown. In which direction would an electric field also make an electron move downwards?

Feb/March 2024

On Fig. 8.2, draw three magnetic field lines to show both the field direction and how the strength changes with distance from the wire.

Feb/March 2024

A copper wire is placed in a uniform magnetic field. What change produces an induced electromotive force (e.m.f.) in the wire?

Feb/March 2025

A wire is moved within the space between the poles of a magnet. A current is induced in the wire. In which direction is the wire moved?

Feb/March 2025

A fixed resistor is attached to the secondary coil of a step-down transformer. The transformer is 100% efficient. The variable resistor is altered so that the current in the fixed resistor falls by $0.25\,\text{A}$. What is the change in the current in the primary circuit?

Feb/March 2025

An electrical device alters the voltage of an electrical supply from $240\ \text{V a.c.}$ to $20\ \text{V a.c.}$. What is the name of this device?

Feb/March 2025

An a.c. generator is arranged with its coil of wire perpendicular to the magnetic field. The coil of wire is then turned slowly to produce an alternating electromotive force (e.m.f.). As the coil rotates, a graph of induced e.m.f. against time is drawn. Which part of the graph shows a rotation of three-quarters of a turn?

Feb/March 2025

Fig. 10.1 illustrates the equipment a student uses to show electromagnetic induction.

Feb/March 2025

Fig. 8.1 shows a metal rod hanging in the magnetic field created by two permanent magnets. The rod is linked to a cell, so a current flows through it.

Feb/March 2025

A powerful electromagnet is used to pull in pins. What occurs when the current in the coil is halved?

May/June 2016

The diagram depicts a transformer. The input voltage is $240\ \text{V}$. What is the output voltage?

May/June 2016

A strong electromagnet is used to pull pins towards it. What happens if the current in the coil is reduced to half?

May/June 2016

The diagram represents a transformer. The input voltage has a value of $240\,\text{V}$. What output voltage is produced?

May/June 2016

A powerful electromagnet is used to attract pins. What occurs when the current in the coil is reduced to half its original value?

May/June 2016

The diagram illustrates a transformer. The primary coil contains 800 turns, while the secondary coil contains 40 turns. An input voltage of $240\,\text{V}$ is supplied. What output voltage is obtained?

May/June 2016

A powerful electromagnet is used to pull pins towards it. What happens when the current in the coil is reduced by half?

May/June 2016

The diagram illustrates a transformer. The input voltage is $240\,\text{V}$. What voltage is produced at the output?

May/June 2016

The diagram depicts a shaded region in which the magnetic field points into the page. A beam of $\beta$-particles enters the field as shown. In what direction is the beam of $\beta$-particles deflected as it enters the magnetic field?

May/June 2016

A powerful electromagnet is used to pull in pins. What happens if the current in the coil is reduced to half its original value?

May/June 2016

The diagram illustrates a transformer. The input voltage has a value of $240\,\text{V}$. What is the output voltage?

May/June 2016

The diagram represents a shaded region in which the magnetic field points into the page. A beam of $\beta$-particles enters the field as shown. As the $\beta$-particles enter the magnetic field, in what direction is the beam deflected?

May/June 2016

A powerful electromagnet is used to pull in pins. What occurs if the current in the coil is reduced to half its original value?

May/June 2016

A transformer is shown in the diagram. The input voltage is $240\,\text{V}$. What output voltage is produced?

May/June 2016

The diagram indicates a shaded region in which the magnetic field points into the page. A beam of $\beta$-particles is moving into the field as shown. As the beam enters the magnetic field, in which direction is it deflected?

May/June 2016

Fig. 10.1 depicts the charger of a laptop computer, and it includes a transformer.

May/June 2016

Calculate the current in the wire.

May/June 2016

Fig. 10.1 illustrates the charger of a laptop computer. A transformer is housed inside the charger.

May/June 2016

Calculate the current flowing in the wire.

May/June 2016

Two vertical straight wires X and Y pass through holes in a horizontal card. Fig. 8.1 shows the card as seen from above. Each wire carries a current downward (into the page).

May/June 2016

The two ends of a metal rod are linked to a very sensitive ammeter by copper wire. The rod is kept horizontal in the horizontal magnetic field between the N-pole and S-pole of a permanent magnet, as shown in Fig. 9.1.

May/June 2016

A coil made from four loops of wire is positioned in a magnetic field. When current flows, the coil feels a turning effect. More loops of wire are then added to the coil, while the current stays the same. How does this change the turning effect?

May/June 2017

A wire is moving in the direction indicated between the poles of a magnet. Which alteration would increase the size of the induced electromotive force (e.m.f.) across the ends of the wire?

May/June 2017

A magnet placed close to a coil of wire is pulled towards the coil only if a current flows in the coil. Which statement accounts for this force of attraction?

May/June 2017

A simple d.c. electric motor has a coil that rotates inside a magnetic field. A commutator links the power supply to the coil. What is the function of the commutator?

May/June 2017

An electric generator has an electromotive force (e.m.f.) of $200\,\text{V}$ and a current of $3.0\,\text{A}$ in a circuit. An engine with a power of $2.4\,\text{kW}$ drives the generator. What is the efficiency of the generator?

May/June 2017

A magnet placed close to a wire coil is pulled towards the coil only if a current flows through the coil. Which statement accounts for this attractive force?

May/June 2017

Which device makes use of a split-ring commutator?

May/June 2017

A magnet positioned close to a coil of wire is drawn towards the coil only when current flows in the coil. Which statement accounts for this force of attraction?

May/June 2017

A steel magnet is inserted into a coil and demagnetised. What kind of current is produced in the coil, and in what way does the current vary?

May/June 2017

In what device is a split-ring commutator used, and what function does it serve?

May/June 2017

A student shows electromagnetic induction.

May/June 2017

A television plug is fitted with a fuse.

May/June 2017

Fig. 9.1 shows a coil that carries current in a magnetic field. The diagram marks the magnets N and S, the coil points A, B, C, and D, the current direction on side AB, the force F on side AB, and the connections to a battery.

May/June 2017

A transformer is attached to a $240\,V$ supply so that the motor receives the correct voltage.

May/June 2017

A bar magnet is constructed from metal.

May/June 2017

Fig. 9.1 depicts a horizontal wire PQ located in the gap between the N pole and the S pole of a magnet. A current flows in the wire from P to Q. Because the wire carries current in the magnetic field, a force acts on it.

May/June 2017

Fig. 10.1 depicts a transformer made up of two coils P and Q, together with an iron core. Coil P has 200 turns and coil Q has 340 turns. A $4.0\,\text{V}$ a.c. power supply is connected to coil P.

May/June 2017

Which of the following statements about electromagnetic induction is correct?

May/June 2018

An electrical device alters the voltage of an electrical supply from $240\ \text{V a.c.}$ to $20\ \text{V a.c.}$. What is this device called?

May/June 2018

A simple electric generator produces an electromotive force (e.m.f.). Which change would make the induced e.m.f. larger?

May/June 2018

For a transformer, the primary coil contains $N_p$ turns and the secondary coil contains $N_s$ turns. Which row shows the values of $N_p$ and $N_s$ for a transformer that increases a voltage of $1200\,\text{V}$ to $36\,000\,\text{V}$?

May/June 2018

A straight wire stands at right angles to the page. The current flows into the page. What magnetic field pattern is produced around the wire, and in which direction does it act nearby?

May/June 2018

The diagram illustrates a transformer. Which materials are best suited for the core and for the coils?

May/June 2018

When a conductor carrying current is placed in a magnetic field, a force acts on it. Which changes cause the force to reverse direction?

May/June 2018