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Physics > P2 - Eletricity > Flashcards

P2 - Eletricity Flashcards

1
Q

What flows in a circuit?

A

electrons in an electric current

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2
Q

Series circuit?

A

Has no branches so current can only flow in one path

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3
Q

Unit of electric current?

A

Ampere (A)

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4
Q

What is conventional current?

A

Even though the current flows from negative end to the positive end of the cell, scientists always draw it in the opposite direction

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5
Q

Potential difference (voltage)?

A

describes the “pressure” that pushes electricity

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6
Q

What is the PD like in a parallel circuit?

A

the voltage across each component on different branches is the same

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7
Q

A battery?

A

two or more cells connected together in the same direction

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8
Q

A current of 1 ampere =?

A

1 coulomb of charge flowing per second

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9
Q

Charge flow (coulombs)=?

A

Current (A) X Time

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10
Q

Energy transferred=?

A

Charge flow (C) X PD (V)

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11
Q

What does a cell in a circuit contain?

A

chemical energy which is transferred to electrical energy

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12
Q

Resistance?

A

opposition to the flow of current

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13
Q

The more energy that is transferred as the current moves (v) …?

A

the higher the resistance

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14
Q

Resistance equation?

A

= PD (V) / current (A)

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15
Q

resistor symbol?

A

-[]- (longer tho)

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16
Q

A resistor?

A

an electrical component that limits the flow of electrical current in a circuit

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17
Q

1 reason that a resistor would be used in a circuit?

A

To dim a lamp in the circuit

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18
Q

What is resistance measured in?

A

Ohms (horseshoe)

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19
Q

What happens to the current (A) if we increase the voltage in a resistor?

A

The current also increases at the same amount (directly proportional)

20
Q

What happens to the resistance if we increase the current?

A

It stays constant (ohmic conductor)

21
Q

What is the only way that resistance will stay constant?

A

if the temperature is constant

22
Q

Why is the current in a filament lamp not directly proportional to the potential difference?

A

Because the filament gets hot, which causes the resistance to increase (not an ohmic conductor)

23
Q

Why does the current in a diode flow in only one direction?

A

Becuase it has a very high resistance in the reverse direction
It will not allow the current to flow through if the cell changes direction

24
Q

What is the most energy-efficient source of light?

A

LED
light emitting diodes

25
Q

Potential Difference equation?

A

Resistance X Current

26
Q

What is the total resistance of two resistors in a parallel circuit?

A

It is less than the resistance of the smallest resistors because there is 2 pathways for the current to take, meaning more total current

27
Q

LDR?

A

Light dependent resistor

28
Q

What happens when LDRs are in dark and light conditions? what happens with the current?

A

Dark conditions= has a high resistance- meaning it takes a great deal of energy for the current to pass through the LDR

Light conditions= very low resistance- meaning it takes very little energy for current to pass though the LDR

29
Q

How does an LDR cause the photo screen to turn off when next to ear?

A

Becuase it’s dark, it takes a great deal of energy for the current to pass through the LDR, causing the lamp in the circuit to become very dim

30
Q

Key feature of a thermistor?

A

The resistance of a thermistor decreases if the temp increases

31
Q

What happens if a computer gets hot? (thermistor)

A

The resistance of the thermistor falls and now take much less energy to pass through it so more PD is available for the fan

32
Q

1 watt=?

A

1 joule per second

33
Q

Which appliances that are designed to generate what energy usually have a much higher power rating (2400W)?

A

Thermal energy appliances

34
Q

Energy transferred=?

A

Power X Time

35
Q

Power in a circuit=?

A

PD X Current

36
Q

What is direct current?

A

When the current from a cell moves round the circuit and returns back in only one direction

37
Q

Alternating current?

A

the current is constantly changing direction

38
Q

What does live wire do? (brown)

A

Carries the alternating potential difference from the supply

39
Q

Neutral wire? (blue)

A

Completed the circuit and has a PD of 0V

40
Q

Earth wire? (green/yellow)

A

Safety wire to stop appliances from becoming live

41
Q

What’s the most dangerous wire to touch?

A

Live wire 230V

42
Q

The national grid?

A

a system of transformers and high voltage cables carrying electricity around the uk

43
Q

In the national grid, why is energy always lost in the power cables?

A

Due to the resistance of the wires

44
Q

How to reduce energy lost in the UK?

A

building power stations near to homes

45
Q

What do step-up transformers do?

A

increase the PD which reduces energy loss in the cables

46
Q

What do step down transformers do in the national grid?

A

take that voltage and reduce it to safer levels for use in household appliances, electronics, industrial equipment, and other applications

Physics (7 decks)

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