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Physics (Triple) > Electricity > Flashcards

Electricity Flashcards

(63 cards)

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1
Q

What is an electrical current?

A

Electrical current is the flow of electric charges.

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2
Q

What is needed for an electric charge to flow?

A

For an electric charge to flow, there has to be a source of potential difference and a closed circuit.

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3
Q

What is the equation for charge?

A

Charge = current x time

Q = I x t

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4
Q

What are amperes (A) the unit for?

A

Electric current

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5
Q

What is an electrical insulator?

A

An electrical insulator is a material that doesn’t allow electric currents to pass through it etc plastic and glass.

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6
Q

What is an electrical conductor?

A

An electrical conductor is a material that allows electric currents to pass through it. All metals are electrical conductors.

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7
Q

Why can electrical conductors conduct electricity?

A
  • An electrical conductor has lots of charges that are free to move.
  • In a metal, the charges that are free to move are electrons.
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8
Q

Why can’t electrical insulators conduct electricity?

A
  • An electrical insulator has no free electrons.
  • No charges are free to move and carry a current.
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9
Q

What is potential difference?

A

Potential difference is the difference in the amount of energy that charge carries have between two points in a circuit.

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10
Q

What instrument do you use to measure potential difference?

A

A voltmeter

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11
Q

What is the equation for potential difference?

A

Potential difference = current x resistance

V = I x R

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12
Q

What is the equation for voltage and energy?

A

Energy transferred = voltage x charge

E = V x Q

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13
Q

What is an ammeter?

A

An ammeter measures the flow of current that passes through it. Ammeters have to be connected in series with the electrical component you are measuring.

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14
Q

What is a voltmeter?

A

Voltmeters measure the potenti difference between two points in a circuit. Voltmeters must always be connected in parallel with the two points being measured.

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15
Q

What is the difference between current and potential difference?

A
  • The current is the flow of charge. Current us measured through a component.
  • Potential difference is the energy used between two points in a circuit, therefore it measures between the two points either side of the component.
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16
Q

What is resistance?

A

Resistance is a measure of how difficult it is for current to flow through a component.

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17
Q

What are the two things that affects the size of the current when charge flow?

A
  • The resistance -> If the resistance is increased, the current will decrease.
  • The potential difference -> If the potential difference is increased, the current will increase.
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18
Q

What is the unit for resistance?

A

Ohms - Ω

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19
Q

What is the equation for resistance?

A

Resistance = potential difference ÷ current

R = V ÷ I

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20
Q

What is a diode?

A

A diode is a component that only allows current to flow through it in one direction.

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21
Q

What is a rectifier?

A

A rectifier is a component that turns an alternating current into a direct current. Diodes act as rectifiers as they block alternating current when it changes direction.

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22
Q

What is a thermistor?

A

A thermistor is a component where resistance changes with its temperature. Usually when temperature increases, resistance decreases.

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23
Q

What is a LDR?

A

A light dependant resistor (LDR)’s resistance changes with light intensity. Usually when light intensity increases, the resistance decreases.

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24
Q

What is the equation for power and current?

A

Power = current x potent difference

P = I x V

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25
What is the unit for power?
Watts (W)
26
What is the unit for potential difference?
Volts (V)
27
What is the unit for current?
Amps (A)
28
What is the equation for total energy transfer?
Energy = Power x time E = P x t
29
What is an ohmic conductor?
An ohmic conductor is a conductor that obeys Ohm's Law.
30
What is Ohm's Law?
The current through an ohmic conductor (at constant temperature) is directly proportional to the potential difference across the resistor. This means that the resistance remains constant as the current changes.
31
What is the equation of resistance (Ohm's Law)?
Resistance = potential difference ÷ current R = V ÷ I
32
How does current change around a series circuit?
It doesn't
33
What is a collection of cells called?
A battery
34
What are the key features of a series circuit?
- All components are attached in a row - The current is equal everywhere in the circuit. - The voltage across each component is different. - The sum of the voltages across each component is the total battery voltage.
35
How does a parallel circuit work?
In a parallel circuit, components are connected on separate branches of wires to the energy source.
36
How do you calculate the total current thorough the energy source in a parallel circuit?
It is the sum of the currents in the individual branches.
37
What quantity is split between branches of a parallel circuit?
The current
38
What are the two types of electric current?
Direct current Alternating current
39
How does direct current work?
- The electric current flows in only one direction. - Batteries and cells are sources of direct current.
40
How does alternating current work?
- Electric current repeatedly changes direction. - In the UK, the electricity from the plug sockets is a source of alternating current. (The mains electricity supply has a frequency of 50Hz and about 230V.
41
What are the characteristics of the neutral wire?
- The neutral wire is blue - It is at or close to earth potential (0V) - It completes the circuit and carries current away from the appliance
42
What are the characteristics of the live wire?
- The live wire is brown - It provides the alternative potential difference from the mains electricity supply.
43
What are the characteristics of the Earth wire?
- The earth wire has green and yellow stripes. - It has a 0V potential and only carries a current if there is a fault. - It is a safety wire to stop the appliance from becoming alive.
44
What is the potential difference across the mains power supply in the UK?
230 V
45
What is the national grid?
The national grid is the network of cables and transformers that connect power stations with houses and shops in the United Kingdom.
46
What do power stations create?
Power stations create an electric current (which is an energy carrier).
47
Why are larger power stations more efficient than smaller power stations?
They can burn lots of fuel at very high temperatures. This creates very hot steam that can turn the turbines. (Steam turbines are more efficient at higher temperatures).
48
How much electricity does a power station produce?
At the voltage of 25,000 volts.
49
What does step-up transformers do?
Step-up transformers then increase the potential difference to 400,000 volts.
50
Why do step-up transformers increase in potential difference?
This reduces the current and hoe much heat is lost when it's being transported across the country, which increases the efficiency of the National Grid system.
51
What do step-down transformers do?
Step-down transformers reduce the voltage to a lower value.
52
Why do step-down transformers reduce voltage?
So electricity is at a safer voltage to enter our homes.
53
How do fuses work?
Fuses contain a thin wire that melts if the current flowing through an appliance is too high, which breaks the circuit and the flow of electric current.
54
How do circuit breakers work?
Circuit breakers are special devices that switch off the flow of current if the current is higher than a certain value. Circuit breakers have the same jobs as fuses but instead can be used multiple times.
55
How do fuses and circuit breakers protect us from electrical appliances?
They stop the flow of electric current if it is gets too high. This stops the appliance overheating.
56
What are fuse ratings?
Fuse ratings tell us the level where a fuse will begin to melt. The fuse chosen should have a value just above the normal current that an electrical appliance uses.
57
Why is a 13 A fuse wrong to use for an appliance with a 3.9 A operating current?
More than 3x the normal operating current needed to melt the fuse. Therefore a 13 A fuse might not even melt if the appliance developed a fault.
58
Earth wires are needed for appliances with what?
Metal casing
59
What kind of charges repel?
Two objects that are both the same charges (both positive or both negative).
60
What kind of charges attract to each other?
Objects that have opposite charges (one negative and one positive).
61
What charge will a material gain if it loses an electron?
Positive
62
How can charged objects exert forces on each other?
- Rubbing an object - Charged rod - Insulated objects
63
What are objects with no conducting path to earth called?
Isolated

Physics (Triple) (7 decks)

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