Electromagnetism

Figure 8 shows iron nails being attracted to a magnet.

Iron is a magnetic material.

Which two of the following are also magnetic materials?

Tick (✓) two boxes.

The iron nails become magnets when they are attracted to the bar magnet.

Complete the sentence.

Choose the answer from the box.

The iron nails become.

Figure 9 shows two bar magnets next to each other.

Figure 9

Which arrow shows the direction of the magnetic field between the magnets?

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Figure 10 shows the direction of the current in a wire.

The current causes a magnetic field around the wire.

Which of the following shows the magnetic field pattern around the wire?

Tick (✓) one box.

What two changes would increase the strength of the magnetic field around the wire?

Some metals are magnetic and others are non-magnetic.

Which of the following metals is magnetic?

Tick (✓) one box.

Figure 1 shows magnetic field lines around a bar magnet.

The circles represent plotting compasses.

Draw one arrow in each circle on Figure 1 to show the direction of the magnetic field at each place.

Figure 2 shows magnetic field lines around a bar magnet.

Which letter shows where the magnetic field is strongest?

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Figure 3 shows the magnetic field lines between two bar magnets.

Which diagram shows how the magnets are arranged in Figure 3 ?

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A teacher demonstrates how a current in a wire creates a magnetic field around the wire.

Figure 4 shows the wire passing through a piece of cardboard.

The current can be switched on and off.

Describe how the teacher can use a plotting compass to demonstrate the magnetic effect of the current in the wire.

The teacher decreases the current in the wire.

How does the strength of the magnetic field around the wire change?

Tick (✓) one box.

The teacher reverses the direction of the current in the wire.

What happens to the magnetic field around the wire?

Figure 5 shows the magnetic field pattern produced when there is a current in a wire.

What do the arrows on the magnetic field lines represent?

How could the strength of the magnetic field be increased? Tick (✓) one box.

The wire is coiled to make a solenoid. Which diagram in Figure 6 shows the magnetic field pattern produced when there is a current in the solenoid?

Figure 7 shows the parts of an electric bell.

Figure 8 shows an incomplete sequence of how the bell works.

Write one letter in each box to show the correct sequence. Use each letter once. A A magnetic field is created around the electromagnet. B A resultant force acts on the iron arm causing it to move towards the electromagnet. C The iron arm returns to its original position. D There is a current in the circuit.

Which of the following would increase the resultant force on the iron arm? Tick (✓) one box.

The iron arm of the bell vibrates with a frequency of 6.25 Hz. Calculate the period of the iron arm. Use the equation:

The sound waves produced by the bell are longitudinal waves. Figure 9 shows the position of the air particles at one point in time as the sound waves travel through the air.

Which letter represents an area of compression? Tick (✓) one box.

When two magnets are close together they exert a force on each other.

Complete Table 1 to show if the magnets would attract or repel.

Tick (✓) one box in each row.

Figure 1 shows the magnetic field around a bar magnet.

Which statements are true for the magnetic field shown in Figure 1 ?

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Figure 2 includes an electromagnet.

Which metal is used to make the core of the electromagnet?

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Complete the sentence.

Choose the answer from the box.

The number of turns on the coil is increased. The current remains the same.

How does this affect the strength of the magnetic field around the electromagnet?

Tick (✓) one box.

The metal core was removed. The current remains the same.

How does this affect the strength of the magnetic field around the electromagnet?

Tick (✓) one box.

Figure 16 shows the magnetic field pattern around a bar magnet.

Draw an arrow at point A and point B to show the direction of the magnetic field at each point.

A bar magnet produces its own magnetic field. Complete the sentence. Choose the answer from the box.

A bar magnet is an example of.

Which graph shows how the strength of the magnetic field varies with distance from the bar magnet? Give a reason for your answer. Tick (✓) one box.

Figure 17 shows an electromagnet being used to separate aluminium cans from steel cans.

Explain how the electromagnet and conveyor belt are used to separate the steel cans from the aluminium cans.

At the top of the table the strength of the magnetic field is only just enough to pick the cans up. Describe two ways to increase the strength of magnetic field at the top of the table.

Write down the equation which links distance travelled (s), speed (v) and time (t).

The conveyor belt moves a can at a speed of 1.7 m/s. Calculate the time taken to move the can 3.3 m at this speed. Give your answer to 2 significant figures.

A student placed a magnet on top of a plastic support in a bowl of water. This magnet was fixed in position and above the surface of the water. The student put a second magnet into a piece of cork so that the magnet floated on the water. Only the north pole of the floating magnet was above the surface of the water. Figure 6 shows the arrangement of the magnets.

The floating magnet was placed near to the north pole of the fixed magnet. The floating magnet then moved along the path shown in Figure 6. Explain why.

The student replaced the floating magnet with a piece of iron. What happened to the piece of iron?

Describe how to use a compass to plot the magnetic field pattern around a bar magnet. Use Figure 7 to help you.

Figure 8 shows a diagram of an electromagnetic lock used to secure a door.

Figure 9 shows an incomplete sequence of how the door unlocks.

Write one letter in each box to show the correct sequence. A The iron bolt moves. B A magnetic field is created around the solenoid. C There is a current in the circuit.

The electromagnetic lock contains a spring. When the door is unlocked the extension of the spring is 0.040 m. spring constant = 200 N/m Calculate the elastic potential energy of the spring when the door is unlocked. Use the equation: elastic potential energy = 0.5 spring constant (extension)²

A door is fitted with a security lens and a lock. The security lens allows a person to see a visitor before opening the door. The security lens is concave.

Figure 5 is an incomplete ray diagram representing a visitor standing near the security lens. Complete Figure 5 to show how an image of the visitor is formed by the concave lens. Draw an arrow to represent the image.

The visitor moves further away from the security lens in the door. How does the size of the image change? Tick (✓) one box.

Figure 6 shows a diagram of the lock. The door unlocks when the switch is closed.

Which material should the bolt be made from? Tick (✓) one box.

Explain why the door unlocks when the switch is closed.

When the door unlocks, a force of 2.88 N is applied to the spring. The spring extends by 1.50 cm. Calculate the spring constant of the spring.

Give two ways the resultant force on the bolt could be increased.

Figure 5 shows a bar magnet. Each circle represents a compass.

Figure 5

Draw an arrow inside each circle to show the direction that each compass would point.

Figure 6 shows part of a coat. The coat has two magnets hidden inside the material. Figure 7 shows how the magnets are used to fasten the coat.

Explain why the magnets inside the coat must not have two south poles facing each other.

A coil of wire is connected to a battery. The current in the coil produces a magnetic field.

Which diagram in Figure 8 shows the magnetic field produced by the current in the coil?

Tick (✓) one box.

Figure 8

A solid rod is placed inside the coil. Which type of rod would make the magnetic field of the coil stronger?

Tick (✓) one box.

A student investigated how the strength of an electromagnet varies with the current in the coil of the electromagnet. Figure 9 shows the equipment the student used.

Figure 9

Why does the spring get longer when the electromagnet is switched on?

The student measured how much further the spring extended with different values of current in the coil. Figure 10 shows the results.

The current in the coil is increased from 0.6 A to 1.2 A Determine the increase in the extension of the spring.

Calculate the increase in the force on the spring when the current in the coil increased from 0.6 A to 1.2 A Spring constant = 0.18 N/cm Use the equation: force = spring constant × extension

Describe what happened to the strength of the electromagnet as the current in the coil increased from 1.2 A to 1.6 A

Figure 5 shows a solenoid. Draw the magnetic field of the solenoid on Figure 5.

Figure 5

Figure 6 shows two iron rods placed inside a solenoid.

Explain why the iron rods move apart when the switch is closed.

A student investigated the strength of an electromagnet. The student investigated how the strength depended on:

• the current in the wire

• the number of turns of wire around the iron core.

Figure 7 shows the equipment used.

The student measured the strength of the electromagnet as the maximum weight the electromagnet could hold.

Table 1 shows the results.

Explain why the method used by the student is not valid for this investigation.

A second student repeated the investigation using the same equipment. Figure 8 shows the second student’s results.

How does increasing the current in the wire affect the strength of the electromagnet, when the electromagnet has 30 turns of wire?

How does increasing the number of turns of wire from 10 to 20 affect the strength of the electromagnet, compared to increasing the number of turns of wire from 20 to 30?

Figure 3 shows two paper clips hanging from a bar magnet.

The paper clips have become magnetised.

Label the north and south poles of both paper clips.

A student investigated how the number of turns of wire on an electromagnet affects the strength of the electromagnet. Figure 4 shows the equipment used by the student. Throughout the investigation the student kept the current through the wire constant.

The student measured the strength of the electromagnet by counting the number of paper clips the electromagnet could hold. Explain why it was important that the paper clips were all the same size.

Table 2 shows the student’s results.

Describe the pattern shown in Table 2.

The student then used 50 turns of wire on the electromagnet. The electromagnet picked up 18 paper clips. This was more paper clips than the student had expected. Which one is the most likely cause of this result? Tick one box.

The student repeated the measurement for 50 turns of wire three more times. This gave her the following set of results. 18 16 14 15 Explain what the student should now do with the four results for 50 turns of wire.

The student wrote the hypothesis: ‘Increasing the current through the wire will make the electromagnet stronger.’ Describe how the student should change the investigation to test this hypothesis.

The circle in Figure 18 represents a straight wire carrying a current. The cross shows that the current is into the plane of the paper.

Figure 18

Complete Figure 18 to show the magnetic field pattern around the wire.

The magnetic flux density 10 cm from the wire is 4 microtesla. Which of the following is the same as 4 microtesla? Tick one box.

Figure 19 shows a simple electric motor.

Figure 19

When there is a current in the coil, the coil rotates continuously. Explain why.