Electricity and Magnetisum

Question 1

Negatively Charged

Answer 1

Gain electrons, so an excess amount of electrons.

Question 2

Positively Charged

Answer 2

Lost electrons, so an excess amount of protons.

Question 3

Conductor

Answer 3

Substance in which electrons can move freely e.g metals

The charge is spread out over the surface evenly because of the electron transfer. More electrons at the corners than a flat surface due to electron movement.

Only conductors can be charged by contact.

Question 4

Insulator

Answer 4

Substance in which electrons cannot move freely e.g plastics

Only the part that becomes rubbed is charged.

Only insulators can be charged by friction.

Question 5

Charging by Friction

Answer 5

Objects become electrically charged by being rubbed together, electrons are transferred from one object to another, objects gain equal but opposite charges.

Question 6

Charging by Contact

Answer 6

Uncharged objects can become charged by coming into contact with other charged objects. They will gain the same type of charge as the charged object.

Question 7

Earthing

Answer 7

The Earth is a conductor and because of its large size can be considered to be an infinite store of charge, If a charged object is connected to the Earth via a conductor, electrons will flow to, or from, the Earth in order to discharge it.

Question 8

Electrical discharge to the air

Answer 8

Over time electrons will gradually be lost to (or gained from) the molecules in the air. This happens more quickly if the air is humid.

Question 9

In a series circuit, the current …

Answer 9

… is the same though out

Question 10

In a parallel circuit, the current…

Answer 10

… splits up

Question 11

In a series circuit the voltages around the circuit…

Answer 11

… add up to the supply voltage

Question 12

In a parallel circuit each branch receives…

Answer 12

… the same voltage

Question 13

Voltage (V)

Answer 13

Voltage is a measure of how much energy electrons gain or lose around a circuit.

Question 14

Current (I)

Answer 14

Electrical current is the rate of flow of electrical charge (usually electrons).

Question 15

Fuses

Answer 15

A fuse is a safety device that prevents currents becoming too high in a circuit. They are a piece of metal wire that heats up as the current increases.

Question 16

Electrical Power (P)

Answer 16

The power of an electrical device tells us how much electrical energy it converts into other forms of energy each second. Measured in Watts (W)

Question 17

Magnetism

Answer 17

A magnetic field is a region where magnetic forces can be detected. The field lines:

• show the direction of the force on the North Pole of a magnet if it were to be placed in the field
• are close together where the field is strongest

Question 18

Magnetic Field Strength (B)

Answer 18

The strength of a magnetic field has the symbol, B, and the units of Tesla (T)

Question 19

Electromagnetism

Answer 19

When charged objects, such as electrons, move they create a magnetic field around them.

Conventional Current - the original direction current was thought to flow ( + ==> - )

Electron Flow - the actual directions the electrons move (- ==> +)

Question 20

Solenoids

Answer 20

If a wire is coiled up to form a solenoid the magnetic field around each turn of wire interacts to create a stronger field. The direction of the field will depend on the direction that the current flows. Right hand ruled (thumb points to north)

Question 21

Electromagnets

Answer 21

If the solenoid is given an iron core then the strength of the magnetics field will be further increased - an electromagnet has been created.

“Soft” iron means that it loses its magnetism when the current is switched off.

“Hard” iron remains magnetised

Question 22

Paying for Electricity

Answer 22

The joule is a very small amount of energy and so another unit of energy is used by power companies, the kilowatt-hours (kWh).

kWh = kW / h

Cost = (kWh used) x (cost per kWh)

Question 23

Applications of Electromagnets

Answer 23

Relays

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