P7 Electromagnetism

Question 1

What happens when a current flows through a wire

Answer 1

A magnetic field is created around the wire

Question 2

What is a magnetic field made up of?

Answer 2

Concentric circles perpendicular to the wire in the centre

Question 3

What happens to the magnetic field if you change the direction of the current?

Answer 3

The direction of the magnetic field changes

Question 4

What affects the strength of the magnetic field produced?

Answer 4

The current and the distance from the wire determines the strength of the field

Question 5

Solenoid

Answer 5

Wrapping wire into a coil

Question 6

What are solenoids used for?

Answer 6

To increase the strength of the magnetic field that a wire produces

Question 7

Why does a solenoid work?

Answer 7

• The field lines around each loop of wire line up with each other
• This results in lots of field lines pointing in the same direction that are very close to each other

Question 8

What are some other ways to increase the field strength of the solenoid even more?

Answer 8

• Iron core

- It becomes an induced magnet

Question 9

Electromagnet

Answer 9

A solenoid with an iron core whose magnetic field can be turned on and off with an electric current

Question 10

What is needed to experience the full force of a magnetic field?

Answer 10

The wire has to be perpendicular to the magnetic field, otherwise if it runs parallel it won’t experience any force at all

Question 11

Motor effect

Answer 11

• A current carrying wire is put between magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in
• It causes the magnet and the conductor to exert a force on each other
• This can cause the wire to move

Question 12

Give a way of showing the direction of the magnetic force?

Answer 12

• Apply a current to a set of rails inside a horseshoe magnet
• A bar is placed on the rails, which completes the circuit and generates a force that rolls the bar along the rails

Question 13

What are the 3 factors that affect the force acting on a conductor in a magnetic field?

Answer 13

• Magnetic flux density (how many field lines there are in a region and shows the strength on the magnetic field)
• The size on the current
• The length of the conductor that’s in the magnetic field

Question 14

Equation to work out force acting on it when the current is perpendicular to the magnetic field it is in

Answer 14

Force = Current * Magnetic flux density * Length

Question 15

What us Fleming’s left-hand rule?

Answer 15

The direction of the force that is exerted on any current-carrying conductor in a magnetic field

Question 16

Fleming’s left hand rule how to use

Answer 16

• Left hand point your first finger in the direction of the magnetic field
• Point your second finger in the direction of the current
• Your thumb will then point in the direction of the force

Question 17

Split ring commutator in a dc motor

Answer 17

A way of swapping the contacts every half turn to keep the motor rotating in the same direction

Question 18

How to change the direction of the motor?

Answer 18

Swapping the polarity of the dc supply or swapping the magnetic poles

Question 19

How to increase the speed of the motor?

Answer 19

• Increasing the current

- Adding more turns to the coil or increasing the magnetic flux density