Electricity- electric change

Question 1

what is a component

Answer 1

a device in a circuit such as lamp

Question 2

what is electric current

Answer 2

the flow of electrical charge

Question 3

what is voltage or potential difference

Answer 3

the energy transferred per electron

Question 4

what is resistance

Answer 4

• anything that slows the flow of electric charge down

Question 5

charge equation

Answer 5

Q = I (Current) t (time)

Question 6

what equation links current, voltage and resistance

Answer 6

V= IR

Question 7

What does a diode do

Answer 7

allows current to flow in one direction only. Current will not flow in the other direction

Question 8

what is a diode used for

Answer 8

to convert an alternating current into a direct current

Question 9

what is a alternating current ac

Answer 9

an electric current that regularly changes size and direction

Question 10

what is a direct current dc

Answer 10

an electric current that moves in one direction

Question 11

what is electrical current

Answer 11

flow of electrons

Question 12

how can we measure the current through a component

Answer 12

place an ammeter in series with that component

Question 13

how can we measure voltage across a component

Answer 13

a voltmeter must be placed in parallel with that component

Question 14

what is the equation linking voltage, charge and energy transferred

Answer 14

voltage = energy transferred/ charge

Question 15

what is an electric insulator

Answer 15

a material that does not let electric current through it

Question 16

examples of electric insulators

Answer 16

• plastic
• rubber
• glass

Question 17

why can’t electric insulators conduct electricity

Answer 17

because they have no free electrons so no charges are free to move and carry charge

Question 18

why can electric conductors conduct electricity

Answer 18

An electrical conductor has lots of charges that are free to move.
In a metal, the charges that are free to move are electrons.
The electric current through the metal is the flow of these free electrons.

Question 19

what must voltmeters be connected in

Answer 19

parallel

Question 20

what must ammeters be connected in

Answer 20

series

Question 21

how do lengths of wires affect resistance

Answer 21

the longer a wire, the higher the resistance

Question 22

what is a thermistor and its properties

Answer 22

a component where resistance changes with temperature
- resistance decreases as temperature increases
- high temps = low resistance
- low temps = high resistance

Question 23

what is a LDR and its properties

Answer 23

a component where resistance changes with light intensity, increasing light intensity decreases resistance

• in dark conditions, resistance is high
• in light conditions, resistance is low

Question 24

equation linking energy power and time

Answer 24

energy transferred = power x time

Question 25

equation linking power, voltage and current

Answer 25

P = I x V.
We know V = IR, so power can also be calculated by:
P = I^2R

Question 26

what makes current flow

Answer 26

the energy source ( battery etc)

Question 27

what is ohms law

Answer 27

The current through an ohmic conductor is directly proportional to the potential difference across the resistor.
This means that the resistance remains constant as the current changes.

Question 28

w What happens if we close the switch?

Answer 28

A current can flow through the circuit

Question 29

what are diodes used for

Answer 29

to control the flow of current in circuits

Question 30

examples of how ldrs are used

Answer 30

• to detect light
• to turn pff a phone when ur on a call
• in the light, the resistance of the LDR is very low, meaning it takes very little energy for the current to pass through the LDR
• because of this the pd across the ldr is very low
• because potential difference is shared between components in series, the pd across the lamp is large
• if the phone is held to a persons ear, the ldr is in darkness and the resistance of the ldr rises sharply. now it takes a great deal of energy for current to pass through the ldr so pd across it is very high
• meaning theres less electrical energy for the lamp

Question 31

how are thermistors used

Answer 31

• in thermostats in computers to reduce them getting hot
• curcuit usually has a fan
• thermistor is connected in series to the cooling fan
• under cool conditions, the resistance of the thermistor is high, meaning it takes a lot of energy for the current to pass through thermistor
• because of that the pd across the thermistor is high and pd across the fan is small
• if computer gets hot, the resistance of thermistor falls, takes much less energy for the current to pass through thermistor
• this means pd across the thermistor is very low so more electrical energy is available for the fan
• this makes the pd of the fan very high so that it can be warmth