Electromagnetism

This question is about electromagnets.

Describe the construction of a simple electromagnet that is producing a magnetic field.

You may draw a diagram to help your answer.

A proton moves through a uniform magnetic field produced by a strong electromagnet.

The shaded area in the diagram represents the magnetic field.

The initial velocity, v, of the proton is also shown.

Use the left-hand rule to determine the direction of the force acting on the proton.

Explain how the force on the proton changes as the proton moves through the magnetic field.

You may add to the diagram to help your answer.

Suggest why the velocity of the proton changes.

This question is about a filament lamp.

Which of these is the correct circuit symbol for a filament lamp?

The filament lamp emits visible light.

The table gives some statements about visible light.

Place ticks () in the boxes to show which statements are correct for visible light.

The diagram shows a ray of light from the filament lamp incident on the reflective side of a curved mirror.

Complete the diagram by drawing

the normal line where the ray is incident on the mirror.

the reflected ray of light.

The filament lamp is connected in a circuit with a switch and a battery of three cells.

When the switch is on, the filament lamp transfers 120 J of energy in a time of 3.0 minutes.

Each cell has a voltage of 1.5 V.

Calculate the current in the filament lamp.

A small plotting compass is placed near the wires in the circuit.

When the switch is turned on, the compass needle moves to a new position.

Give a reason why the compass needle moves.

A device called a metal detector can be used to find metal buried underground.

The metal detector has two circuits, each containing a coil of copper wire.

Diagram 1 shows the circuit for the transmitter coil.

Suggest why there is a magnetic field around the transmitter coil.

The cell supplies direct current (d.c.). The electronics in diagram 1 change the direct current into alternating current (a.c.) in the coil.

Describe the difference between direct current (d.c.) and alternating current (a.c.).

Diagram 3 shows the circuit for the receiver coil.

As a result of the alternating current in the gold ring, there is an alternating current in the receiving coil.

Explain how an alternating current in the receiving coil causes a sound to be emitted from the loudspeaker.

This question is about electromagnetism.

Diagram 1 shows the magnetic field around a straight section of copper wire.

Explain why the copper wire has the magnetic field shown in the diagram.

A student investigates how the strength of an electromagnet varies with the current in the electromagnet.

The diagram shows their apparatus.

This is the student’s method.

• switch on the electromagnet at its maximum current

• place a load of 100 g so that it is held above the floor by the electromagnet

• slowly reduce the current in the electromagnet until the load falls from the electromagnet

• record the current at which the load falls

• record the current at which the same load falls two more times

Repeat the method for loads of different masses.

Suggest a suitable safety precaution for the student’s investigation.

The table shows the student’s results.

Calculate the mean current when the mass of the load was 600 g.

Give your answer to a suitable number of significant figures.

On the grid, plot a graph of the mean current against the mass of the load.

The scale for the mass axis has been done for you.

Draw the line of best fit.

The student predicts that a load of 1.0 kg will fall when the current in the electromagnet is 3.0 A.

Comment on the student’s prediction.

The diagrams show some equipment that the physicist Ørsted used in an investigation in 1820.

Diagram 1 shows the position of eight compass needles around a wire with no current in the wire.

The compass needles line up with and show the direction of the Earth’s magnetic field lines.

Diagram 2 shows the position of the same compass needles when a current is in the wire.

Diagram 2

Explain why the compass needles turn when the current is switched on.

Using evidence from the compass needles in diagram 2, draw on diagram 2 the shape and direction of a magnetic field line produced by the current in the wire.

Suggest what happens to the magnetic field when the current in the wire is reversed.

The current in the wire is turned off.

Diagram 3 shows the wire placed in a uniform magnetic field.

Diagram 3

The current is now switched on.

Draw an arrow to show the direction of the force on the wire.

The power supply in diagram 3 is replaced by an ammeter.

When the wire is moved, a current is detected.

Explain which direction the wire is moved in the magnetic field to produce a current in the wire.

Explain why a current is produced in the wire when the wire is moved in the magnetic field.

This question is about magnetic fields.

A student positions a thick wire vertically through the centre of a horizontal card.

The student then passes a constant current through the wire in the downward direction, as shown in diagram 1.

On diagram 1, draw the shape and direction of the magnetic field produced by the current in the wire.

Describe a method the student could use to show the shape of the magnetic field produced by the current in the wire.

The student then removes the card and sets up a second wire next to the first wire, as shown in diagram 2.

The current in both wires is in the downward direction.

The student observes that the wires move towards each other.

Explain why the wires move towards each other.

A student investigates how the strength of the magnetic field from a solenoid changes with distance from the end of the solenoid.

The diagram shows the solenoid connected to a power supply.

The student uses a device called a Hall probe, which can be placed anywhere in the magnetic field to measure its strength at that point.

Design a suitable method for the investigation.

Your answer should include

• any extra measuring equipment needed

• details of the independent variable, dependent variable and any control variables

You may include a diagram to help your answer.

The graph shows the results of the student’s investigation.

The student suggests that the relationship linking the strength of the magnetic field and the distance from the end of the solenoid is

strength of magnetic field (distance)³ = constant

Use readings from the graph to deduce whether the results of the student’s investigation support this relationship.

Magnetic Resonance Imaging (MRI) machines can take scans of the inside of a patient.

There is an electromagnet inside the MRI machine.

Describe the construction of an electromagnet.

You may draw a diagram to help your answer.

During the scan, music can be played through a loudspeaker to the patient.

The oscilloscope trace in the diagram represents a sound played to the patient.

Determine the period of the sound wave.

Calculate the frequency of the sound wave.

Deduce whether humans can hear the sound wave.

The current in the loudspeaker is alternating current (a.c.).

Give the evidence from the oscilloscope trace to support this statement.

Draw the circuit symbol for an a.c. power supply.

This question is about electromagnetism.

Diagram 1 shows the construction of an electromagnet.

Name a suitable metal for the core.

State what must be done to the coil of wire to produce a magnetic field.

Electromagnets are used in transformers to change the size of a voltage.

Diagram 2 shows the construction of a simple transformer.

primary coil (1500 turns) secondary coil (280 turns)

Diagram 2

State the formula linking the input (primary) voltage, output (secondary) voltage and the turns ratio for a transformer.

The input voltage to the transformer is 115 V.

Show that the output voltage is approximately 20 V.

The input current to the transformer is 1.2 A.

Calculate the output current.

Assume that the transformer is 100% efficient.

output current =_........

State two factors that would increase the output current of the transformer.

Diagram 1 shows a loop of wire connected to a power supply.

Describe how to find the shape of the magnetic field produced by the loop of wire.

Diagram 2 shows the view from above the card with two cross-sections of the loop of wire.

Key

Diagram 2

On diagram 2, draw the magnetic field produced by the two cross-sections of the loop of wire.

These diagrams show the magnetic field acting on a cross-section of wire when the current in the wire is out of the page.

Which diagram shows the correct direction of the force acting on the cross-section of wire due to the magnetic field?

The magnetic field acting on the cross-section of wire is produced by the current in the other side of the loop of wire.

Explain why there is no effect on the direction of the force on the cross-section of wire when the direction of the current in the loop is reversed.

A machine called the synchrocyclotron (SC) was designed to cause protons to move in a circular path using strong magnetic fields.

The SC used electromagnets to produce the strong magnetic fields.

Describe the construction of a simple electromagnet.

You may draw a diagram to support your answer.

The diagram shows a proton moving at velocity v in the magnetic field produced by the SC.

The direction of the magnetic field is into the page.

Using the left hand rule, determine the direction of the force acting on the proton due to the magnetic field.

The SC is surrounded by very thick concrete walls.

The radiation produced by the SC created atoms of radioactive barium-133 in the concrete walls.

Barium-133 has a half-life of 10.5 years.

State what is meant by the term half-life.

In 1990, the SC stopped being used at CERN, a research centre.

In 1990, the largest number of barium-133 atoms were found 40 cm deep in the concrete walls.

Since 2014, members of the public have been allowed to visit the SC at CERN.

Explain why the radioactive barium-133 in the concrete walls is not a risk to people visiting the SC.

This question is about magnetic fields.

Diagram 1 shows a positively charged proton moving downwards in a uniform magnetic field.

magnetic field

Diagram 1

The proton experiences a force to the right.

What is the direction of the magnetic field?

When a current passes through a flat circular coil, a magnetic field is produced.

Complete diagram 2 by drawing the magnetic field of the flat circular coil.

Diagram 2

A wireless charging base uses a magnetic field to charge the battery of a mobile phone.

There is an alternating current in a coil of wire in the charging base.

There is another coil of wire connected to the battery in the mobile phone.

Explain how the wireless charging base charges the battery of the mobile phone.

Discuss the advantages and disadvantages of using a high current in the wireless charging base.