practice questions

Question 1

what type of magnet is a bar magnet an example of?

Answer 1

a permanent magnet

Question 2

describe the relationship between distance and strength of a magnetic field

Answer 2

as distance increases, the strength of a magnetic field becomes weaker

Question 3

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

Answer 3

• steel cans are attracted to the electromagnet and are transferred to the container
• aluminium cans are not attracted to the electromagnet and are left behind on the table

Question 4

describe two ways to increase the strength of magnetic field at the top of the table

Answer 4

• raise the height of the table
• use a stronger electromagnet or use a larger current

Question 5

why is the core made of iron?

Answer 5

iron is easily magnetised and demagnetised

Question 6

why is steel, not iron, used to make permanent magnets?

Answer 6

magnetised steel does not lose its magnetism easily

Question 7

describe how electromagnets are used in a scrapyard crane

Answer 7

• scrap vehicles are lifted in a scrap yard using powerful electromagnets attached to cranes
• the steel frame of a vehicle sticks to the electromagnet when current passes through the coil of the electromagnet
• when the current is switched off, the vehicle frame falls of the electromagnet

Question 8

explain how an electromagnet is used in a circuit breaker

Answer 8

• a circuit breaker is a switch in series with an electromagnet
• the switch is held closed by a spring
• when the current is too large, the switch is pulled open by the electromagnet
• and it stays open until it is reset manually

Question 9

suggest three changes that would decrease the force acting on the wire

Answer 9

• less current in the wire
• weaker field
• rotation of magnets so field is no longer perpendicular to the wire

Question 10

what type of system uses a liquid to transmit a force?

Answer 10

hydraulic system

Question 11

explain why a loudspeaker cone vibrates when an alternating current flows through the coil

Answer 11

• alternating current creates a magnetic field around the coil
• this magnetic field interacts with the permanent magnetic field
• this produces a resultant force and the coil moves
• when the direction of the current changes, the direction of the force changes to the opposite direction

Question 12

explain how the ignition circuit works

Answer 12

• closing the ignition switch causes a current to pass through the electromagnet
• the iron core becomes magnetised
• the electromagnet attracts the iron arm
• the iron arm pushes the starter motor contacts together
• the starter motor circuit is complete
• a current flows through the starter motor which then turns

Question 13

explain how a driver wearing a seat belt reduces the risk in the event of an accident

Answer 13

• seat belts are designed to stretch
• this increases the impact time
• so reduces the impact force
• seat belts spread the impact force across the chest

Question 14

name two features in a car that reduces injury, other than seat belts

Answer 14

• crumple zones
• padded interior
• roll cage
• air bag

Question 15

what is a force?

Answer 15

a push or pull acting on an object due to the interaction with another object

Question 16

Describe the life cycle of stars much more massive than the Sun, including the formation of new elements.

Answer 16

• fusion processes in stars produce new elements
• cloud of gas and dust (nebula) pulled together by gravitational attraction
• causing increasing temperature to start the fusion process and become a protostar
• hydrogen nuclei fuse to form helium nuclei and the star becomes main sequence
• hydrogen begins to run out and helium nuclei fuse to make heavier elements up to iron
• the star expands to become a red super giant
• the star collapses rapidly and explodes called a supernova
• creating elements heavier than iron
• and distributing them throughout the universe
• leaving behind a neutron star or a black hole

Question 17

which property of a star does the range of wavelengths depend on?

Answer 17

temperature

Question 18

The alternator from the portable power supply is disconnected from the transformer and
lamp. Explain why the handle of the alternator becomes much easier to turn.

Answer 18

• there is no induced current
• so no magnetic field
• to oppose the movement of the coil