P5 Key Facts

Question 1

what is a build up of static charge caused by?

Answer 1

friction

Question 2

what is static charge?

Answer 2

when two insulating materials are rubbed together, negatively charged electrons scrap off one and are put on the other meaning the material that gained the electron is negative and the other is positive.

Question 3

what are charged particles called?

Answer 3

ions (when electrons are removed or gained)

Question 4

what is current?

Answer 4

A movement of charge that can used to power things

Question 5

how does current flow around a circuit?

Answer 5

the metal conductors (wires and components) are full of electrons that are free to move and therefore able to carry the current

Question 6

What does a component need for a current to flow through it?

Answer 6

A voltage

Question 7

What is voltage?

Answer 7

The driving force that pushes the current around the circuit - also the measure of work done to the charge that passes through (how big the push)

Question 8

if you need to measure the voltage of a component, where do you place the voltmeter?

Answer 8

paralle to the component

Question 9

what is voltage?

Answer 9

The potential difference between two points in a circuit - it is also a measure of work done on or by a charge

Question 10

what is a voltmeter used for?

Answer 10

to measure the voltage or potential difference between two points

Question 11

why must a voltmeter be placed in parallel with a component?

Answer 11

so it can compare the energy the charge has before and after passing through the component

Question 12

Hoe do resistor work?

Answer 12

when electrons move through a resistor, they collide with stationary positive ions in the resistor - these collisions make the ions vibrate more which increases the temperature

Question 13

How do filament lamps work?

Answer 13

they contain a piece of wire with a really high resistance , when current passes through it its temperature increases so much that it glows - this is the light that we see

Question 14

what are light dependant resistors?

Answer 14

it changes the resistance depending on how much light there is:
in bright light, resistance falls
in darkness, the resistance increases

Question 15

what are thermistors?

Answer 15

it changes resistance depending on the temperature:
in hot conditions, resistance drops
in cold conditions, the resistance is highest

Question 16

what happens to the PD in a series circuit?

Answer 16

it is shared between the various components so the potential difference round a series circuit always adds up tot eh equal PD across the battery
- total work done to charge by battery is equal to work done to components by charge

Question 17

what happens to the current in a series circuit?

Answer 17

it is the same everywhere in the circuit

Question 18

what is the size of the current determined by?

Answer 18

the total PD (voltage) of the cells and the total resistance of the circuit

Question 19

what happens if the resistance of one component is changed?

Answer 19

the potential difference across all the components will change too

Question 20

what happens to the current when adding cells in series?

Answer 20

it doesn’t change - it will just be the same as if you have one cell in the circuit

Question 21

what happens to the current when adding cells in parallel?

Answer 21

the total current increases but the current through each cell decreases because they join together to make the total current

Question 22

how are components connected in parallel circuits?

Answer 22

they are separately connected to the positive and negative of the supply (if one is removed it will hardly affect the others)

Question 23

what is the PD in parallel circuits?

Answer 23

the PD across each component is equal to the PD across the battery, this means the PD must be the same across all components (all bulbs will be same brightness)

Question 24

what happens to the current in parallel circuits?

Answer 24

the total current leaving the battery is equal to the total currents in the separate branches - the total current going into a junction is equal to the total current leaving the junction

Question 25

what happens to resistance in a parallel circuit?

Answer 25

the resistance is lower because the charge has more than one branch to take - only some of the current will flow along each branch

Question 26

what current will the component with the least resistance have?

Answer 26

the component with the least resistance has the largest current

Question 27

what is the uk mains domestic electricity supply

Answer 27

230 volts

Question 28

what is an AC supply?

Answer 28

an alternating current that is constantly changing direction.
This is what mains electricity is because its easier to generate and easier to distribute over own distances.

Question 29

What is a DC supply?

Answer 29

A direct current that always flows in the same direction.

This is what a batteries supply is.

Question 30

how can the direction of voltage in a coil be changed?

Answer 30

• the voltage is induced in the opposite direction depending on wether you put the magnet in or out the coil
• if the magnets north-south pole polarity is reversed, the voltage is induced in the opposite direction as the opposite pole is pointing out of the coil

Question 31

what is an AC current in a generator?

Answer 31

if the magnet keeps turning in the same direction then the voltage keeps on reversing ever half turn so an AC current is produced

Question 32

how can you increase the size of an induced voltage?

Answer 32

• add an iron core inside the coil
• increase the strength of the magnetic field
• increase the speed of rotation (magnet)
• increase the number of turns in the coil

Question 33

What are transformers used for?

Answer 33

to change the size of and AC voltage

They use electromagnetic induction to step up or step down the voltage

Question 34

How do transformers work?

Answer 34

The alternating current in the primary coil causes changes in the cores magnetic field, this then induces a changing voltage in the secondary coil

Question 35

what is a step up transformer?

Answer 35

They increase the voltage as they have more turns on the secondary coil rather than the primary one

Question 36

what is a step down transformer?

Answer 36

They decrease the voltage as they have more turns in the primary coil rather than the secondary

Question 37

what is Flemings left hand rule?

Answer 37

• the thumb pointing up wards represents the resulting force or motion
• the first finger represents the direction if the magnetic
  field
• the second finger represents the direction of the current in the wire

Question 38

what is the motor effect?

Answer 38

when a rectangular coil of wire carrying a current is placed in a uniform magnetic field, this creates a force which causes the coil to turn
(Left hand rule can be used to see which way coil will turn)

Question 39

how does the coil in an electric motor rotate?

Answer 39

the coil is on a spindle which causes the forces to act on upwards and one downwards, causing a rotation

Question 40

What does a split ring commutator do in an electric motor?

Answer 40

it reverses the direction of the current every half turn to keep the coil rotating continuously in the same direction.

Otherwise, the direction of for would reverse every half turn and the coil would change direction instead of doing a full rotation.

Question 41

How can objects that use rotations be powered by an electric motor?

Answer 41

By connecting the pat of the object that rotates to the motor with an axle