Electromagnetism

Question 1

Define magnetic field

Answer 1

A region of space within which a magnet experiences a force

Question 2

Define plotting compass

Answer 2

A small compass used to find shape of a magnetic field

Question 3

What are magnetic field lines

Answer 3

Lines drawn to represent a magnetic field

Question 4

Where are the strongest points if the magnets

Answer 4

The poles (north and south)

Question 5

Define solenoid

Answer 5

A coil of wire carrying an electrical current

Question 6

Name the magnetic materials

Answer 6

Nickel, steel, iron and cobalt

Question 7

In what direction do field lines always travel in

Answer 7

Flow from north to south

Question 8

Properties of field lines

Answer 8

Never touch or cross
Crowd together in regions where field is strongest.

Question 9

What is the right hand grip rule

Answer 9

When we wrap our right hand around the solenoid, fingers in direction of current, the thumb points to the North Pole.

Question 10

How is an electromagnet effected by and increase in current, the amount of turns and the core?

Answer 10

These all increase magnetism

Question 11

Method of practical to investigate effect on magnetism if current is increased in a solenoid

Answer 11

Construct an electromagnet
Connect to circuit with a battery, an ammeter and a rheostat. Have the same number of turns and increase the amps and count number of paper clips lifted by electromagnet.

We can do this to measure the effect of number of coils and the material of the core.

Question 12

What does the thumb direction represent in Flemings left hand rule?

Answer 12

Force

Question 13

What does the first finger represent in Flemings left hand rule

Answer 13

The magnetism direction

Question 14

What does the second finger represent in Flemings left hand rule

Answer 14

The current direction

Question 15

How does a simple dc motor work?

Answer 15

Applying Flemings left hand rule. Split ring commutator provide contact with power supply. Allows for positive and negative sides to not change when motor spins.

See page 12 of book or watch cognito vid

Question 16

What instrument is used to demonstrate differences between A.C and D.C

Answer 16

Cathode Ray Oscilloscope

Question 17

What is a d.c current

Answer 17

One that always flows in the same direction, from a fixed positive terminal to a fixed negative terminal.

Question 18

What is an A.C current

Answer 18

One in which the voltage and hence current changes size and direction in a regular and repetitive way.

Question 19

When is force in a current carrying conductor in a magnetic field strongest

Answer 19

When current, and field directions are perpendicular

Question 20

Define electromagnetic induction (EMI)

Answer 20

Electromagnetic induction is the production of a voltage across an electrical conductor when the strength of the magnetic field around it changes.

Question 21

Which factors affect the current that flows in an EMI

Answer 21

Moving the magnet faster
Using a stronger magnet
Using a coil with a greater number of turns

Question 22

How is a current induced in a conductor by changing current in a neighbouring conductor

Answer 22

As the conductors are linked magnetically, if an increased magnetic field occurs due to a change in current there will be a small deflection witnessed in the other neighbouring conductor. See Farradays iron ring experiment on pg 121

Question 23

What does a transformer do

Answer 23

They are devices which change the voltage of an a.c supply

Question 24

What is the structure of a transformer

Answer 24

A primary voltage, flows into a primary coil wrapped around a soft iron core which also has another secondary coil wrapped around it which produces a secondary output voltage

Question 25

What is the transformer equation

Answer 25

Vs​➗Vp​​=Ns​➗Np

Question 26

Define a step-up transformer

Answer 26

A transformer in which the output voltage is greater than the input voltage (as output coil had more turns than input coil)

Question 27

Define a step-down transformer

Answer 27

A transformer in which the output voltage is smaller than the input voltage (as output coil has fewer turns than input coil).

Question 28

Why are a.c generators used in electrical generators.

Answer 28

Transformers are used in the process of transporting electricity around the country in order to save energy. Therefore D.C supply cannot be used as it creates a steady magnetic field which does not induce a current to flow just like a magnet held stationary beside a coil.

Question 29

What does a simple a.c generator consist of

Answer 29

A coil rotating between the poles of a magnet

Question 30

What are the main parts of the national grid system

Answer 30

Cooling towers, boilers, Steam turbine, generator, step up transformer, power lines, step down transformer

Question 31

How are step-up and step-down transformers used in transmission?

Answer 31

A step-up transformer boots the voltage up, automatically reducing current value. This conserves power as a smaller current results in less heat energy/power lost from the cables

A step down transformer will then bring the voltage back down to around 240 volts for households