P4 - Electricity✔️

Question 1

Define electric current?

Answer 1

Flow of electrical charge which will only flow round a complete circuit if there is a potential difference - unit of current is ampere, A

Question 2

What is potential difference?

Answer 2

Potential difference or voltage is the driving force that pushes the charge round - units is the volt, V

Question 3

What is resistance?

Answer 3

Resistance is anything that slows the flow down - unit is ohm , Ω

Question 4

What does current flowing through a component depend on?

Answer 4

• potential difference across it
• resistance of the component

Question 5

What are ohmic conductors?

Answer 5

Components where the resistance does not change with current (eg wire or a resistor) - at a constant temperature, the current flowing through an ohmic conductor is directly proportional to the pd across it

Question 6

Give two examples where the resistance of some resistors and components change?

Answer 6

• diode
• filament lamp

Question 7

For diodes what does the resistance depend on?

Answer 7

Resistance depends on the direction of the current - will let current flow in one direction, but have a very high resistance if its reversed

Question 8

Explain what happens when electrical charge flows through a filament lamp?

Answer 8

Transfers some energy to the thermal energy store of the filament, which is designed to heat up - resistance increases with temperature so as current increases (the lamp heats up more) which further increases resistance

Question 9

What does ‘I-V characteristic’ refer to?

Answer 9

Refers to a graph which shows how the current flowing through a component changes as the potential difference acrosss it is increased

Question 10

I-V characteristic of linear components (eg fixed resistor)?

Answer 10

Straight line I-V characteristic

Question 11

I-V characteristic of non-linear components (eg filament lamp, diode)?

Answer 11

Curved I-V characteristic

Question 12

What does LDR stand for?what are there uses?

Answer 12

Light dependent resistor - is dependent on the intensity of light - used for automatic night lights and outdoor lighting

Question 13

Explain the effects of changes in light on resistance of an LDR?

Answer 13

• bright light, the resistance falls
• darkness, the resistance is highest

Question 14

What is a thermistor?what are there uses?

Answer 14

A temperature dependent resistor - which can be useful temperature detectors, eg car engine tempeature sensors

Question 15

Explain the effects of changes in temperature on resistance of a thermistor?

Answer 15

• hot conditions, the resistance drops
• cool conditions, the resistance goes up

Question 16

What is a series circuit?

Answer 16

• Circuit where the different components are connected in a line (end to end) - if you remove or disconnect one component, the circuit is broken and they all stop
• not very handy - very few things are connected in series

Question 17

Relationship between pd in a series circuit?

Answer 17

The total pd of the supply is shared between the various components

Question 18

Relationship between current in a series circuit?

Answer 18

The same current flows through all components - size of the current is determined by the total pd of the cells divided by total resistance of the circuit

Question 19

Relationship between resistance in a series circuit?

Answer 19

You can work out the total resistance of all the components by adding up there resistances together

Question 20

What is a parallel circuit?

Answer 20

• Each component is separately connected to the +ve and -ve of the supply - if you disconnect a component it wont effect the others
• most things connected like this, for example cars and household electrics

Question 21

Relationship between pd in a parrallel circuit?

Answer 21

Pd is the same across all components - because all components get the full source pd which means that all identical bulbs connected in parallel will be at the same brightness

Question 22

Relationship between current in a parallel circuit?

Answer 22

Total current flowing around the circuit is equal to the total of all the currents through the seperate components - you can work out the total current by adding the current flowing through each component

Question 23

Relationship between resistance in parallel circuits?

Answer 23

If you have two resistors in parallel, their total resistance is less than the resistance of the smallest of the two resistors

Question 24

How is static caused by friction?

Answer 24

When certain insulating materials are rubbed together, negativley charged electrons will be scraped off and dumped on the other - leaves the materials electrically charged (one negativley and the other positivley)

Question 25

What dertermines the direction the electrons are transferred when static is built up?

Answer 25

• depends on the two materials involved

Question 26

How can too much static cause a spark?

Answer 26

If the pd gets large enough, electrons can jump across the gap between the charge object and earth - this is the spark

Question 27

explain what causes a static shock?

Answer 27

When the electrons jump to any earthed conductor that is nearby - result of the pd getting too large

Question 28

Define electrostatic attraction?

Answer 28

Non contact force that is a result of oppositely charged electric charges repeling or attracting each other

Question 29

Explain what an electric field is?

Answer 29

Field created around any electrically charged object - the close you get to the object the stronger the field is

Question 30

What happens when a charged object is placed in an electric field?

Answer 30

It feels a force - causes attraction or repulsion as a result of the electric field of each charged object interacting with each other

Question 31

How is a spark caused explain with refrence to electric fields?

Answer 31

Cuased when there is a high enough pd between charged object and the earth - causes a strong electrical field - which causes electrons in the air particles to be ionised - makes air more conductive, so current flows through it - this is the spark