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Physics > SP10- Electricity And Circuits > Flashcards

SP10- Electricity And Circuits Flashcards

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1
Q

Does an atom have a charge

A

No - protons and electrons balance out

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2
Q

Why can metals carry a current

A

Eg sodium has one electron in the outer shell, that is only weakly attracted to the nucleus - these electrons can easily be removed so a metal wire has many “free” electrons

When a battery is attached to the wire the voltage pushes the free electrons around the circuit, electrons are negative so move toward the positive terminal of batttery

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3
Q

What’s the conventional direction of current in diagrams

A

Goes from the positive terminal to the negative terminal of the battery - left to right

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4
Q

Learn the circuit symbols!!

A

Page 141 textbook

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5
Q

What happens in series circuit

A

There is one route the current can take

Lamps can’t be switched on and off inducidually and if one lamp fails - it all switches off

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6
Q

What happens in a parallel circuit

A

There are junctions that allow the current to take different routes

Each lamp can be switched separately

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7
Q

What is current measured in and with

A

Amperes (amps) (A) and with an ammeter

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8
Q

How must an ammeter be connected in a circuit

A

In series

  • to measure the current passing through a component or circuit
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9
Q

What happens to current in a circuit

A

The total amount of current stays the same on its journey around the circuit - battery is the same as the current arriving at the negative termianal

Current is conserved, - in parallel it splits but total is he same still

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10
Q

What do you need potential difference for

A

To “push” current around an electric circuit - it’s also called voltage

Electrons flow when there is a potential difference applied across a circuit

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11
Q

What must there be in order for a current to flow

A

The circuit must be closed and have a source of potential difference - such as a cell of battery

The electrons all move together when a current flows

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12
Q

The bigger the potential difference the ________ the current

A

The bigger the current

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13
Q

How does potential difference change in a circuit

A

In a parallel circuit the potential difference across each branch of the circuit is the same - when there’s more than one component in a branch - the potential difference across all the components add up to give the total voltage supplied by the cell or battery

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14
Q

What way is a voltmeter always connected in parallel with components

A

In parallel

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15
Q

What’s electric charge

A

Moving charged particles to form an electric current, electric charge is measured in coulombs (C) one coulomb is the charge that passes a point in a circuit when there is a current of 1 amp for 1 second

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16
Q

What is the electric current a rate of ?

A

Electric current is the rate of flow of charge

At any point in a circuit, the size of the current tells you how much charge flows paste that point each second

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17
Q

How can charge be calculated

A

Q = I x T

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18
Q

How does the charge have potential energy / how is energy transferred in a circuit

A

The cell/battery transfers energy to the charge, so the charge has potential to transfer energy to other components in the circuit - the charge has potential energy

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19
Q

What’s the potential difference of a cell

A

The amount of potential energy the cell transfers to each coulomb of charge flowing through it

There is a voltage of 1 V when there is 1 joule of energy to each coulomb

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20
Q

How is energy transferred calculated

A

E = Q x V

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21
Q

Why do some wires and components need a larger potential difference to produce a current through them than others

A

They have a large electrical resistance

22
Q

What is resistance measured in

A

Ohms

23
Q

How it resistance calculated

A

V = I x r

24
Q

What happens and why to resisters connected in series

A

The total resistance of the circuit is increased BECUASE the pathway becomes harder for current to flow through

The PD from a cell is shared between the resistors but it may not be shared equally, greater potential difference across resistors with higher resistances

25
Q

What happens and why to resistors in parallel

A

The total resistance of the circuit is less than the resistance of individual resistors - because there are now more paths for the current - the current splits

Potential differences are the same

26
Q

What is a variable resistor used for

A

It’s used to change the current in the circuit , measurements of current and PD can be taken and resistance can be calculated

27
Q

How does PD change across a fixed resistor

A

The current changes by the same percentage - the two variables are in direct proportion, the graph forms a straight line going through the origin - this happens BECUASE resistance stays the same

28
Q

How does potential difference change in a diode

A

They have resistance that changes when pD changes

A diode has a low resistance if the potential difference is in one direction but a very high resistance if the potential difference is in the opposite direction which means current CAN FLOW ONE WAY ONLY IN A DIODE

29
Q

How does pd changes in a filament lamp

A

Causes a current to flow through it, the current causes the filament to heat up and flow, greater the potential difference, more current and hotte and whiter it gets - resistance also increases. When pd changes, current doesn’t change at same percentage

30
Q

How does resistance change with light intensity in LDR (light dependant resister)

A

Has a high resistance in the dark but the resistance gets smaller as the light intensity increases

31
Q

What happens with thermistors and resistance and temperature

A

They have high resistances at low temperatures but as the temperature increases - resistance decreases

32
Q

What happens when electrical work is done against resistance

A

The energy is transferred by heating

When a current passes through a resistor, energy is transferred from heat

33
Q

When is the heating effect in electricity and what happens when it’s not

A

It’s useful in an electric heater or kettle

Not useful in a computer or wired BECUASE it means useful energy is spread out or dissipated
The surroundings gain thermal energy

34
Q

What happens in a resistor

A

As electrons flow through the Lattice of vibrating ions, they collide with ions

The more collisions they make with ions, the more difficult it is for them to pass through - so higher the electrical resistance. When electrons collide with ions, they transfers energy to them

35
Q

How can resistance in circuits be reduced

A

Using wires made from metals with low resistance / such as copper
Thicker wires have power resistance

Can also be decreased by cooling metals so that the lattice ions are not vibrating as much

36
Q

How is energy transferred calculated

A

E = I x V x t

E = P x t

P = I x v

37
Q

What is power

A

Energy transferred per second - often shown as power rating

1 W is 1 joule per second

38
Q

How is power calculated

A

P = energy / time

39
Q

What is power transfer in a component or appliance proportional to?

A

The potential difference across it and the current through it

Power = current x pd

Or power = i^2 x r

40
Q

What source of electricity do large power appliances use

A

Mains electricity - in a power station, energy is transferred from a store of kinetic energy by electricity

Electricity is carried to our homes via cables known as the national grid

41
Q

What is direct current

A

Where a cell has a positive and negative terminal and the movement of charge stays the same

42
Q

What’s alternations current and why is it caused

A

When the direction of current keeps changing - mains electricity is produced using generators that rotate

The voltage also changes - causes it to decrease and peak,

43
Q

Tell me about the uks mains

A

It’s an a.c supply

There are 50 cycles a second - frequency 50 Hz, voltage constantly changing but the average effect is the same as direct current voltage of 230 V

44
Q

What’s 3kW in W

A

3000 W

45
Q

What’s the earth wire in a plug

A

Connects to metal parts of appliance that is attached to a large metal spike or metal tuning that is pushed into the ground - it’s for safety and is at 0V If circuit is correct

Green/ yellow

46
Q

What’s the neutral wire

A

The return path to the power stations

Voltage of 0V

Blue

47
Q

What’s the fuse In a plug

A

A safety device usually marked with the current it can carry

48
Q

What’s the live wire

A

Connects to the appliance to the generators of the power stations

Voltage is 230V

49
Q

Where are switches connected in a circuit

A

In the live wire - when off there’s no current

50
Q

What’s a fuse

A

A tube with a thin wire inside , the current passes through the wire and the wire gets hotter, if the wire exceeds a certain value , the wire melts and so breaks the circuit and stops the current

The fuse melts before wiring or parts of an appliance can overheat - once fault is fixed, a new fuse can be fitted

51
Q

Why is a fuse necessary

A

If a faulty appliance draws too much current, it can cause overheating of the wiring in either the walls or in the appliance - this can cause fires

Metal parts can be at a very high voltage, could get an electric shock if you touched it - a current would flow through you to ground

If fsult causes live wire to touch a metal part - makes a very low resistance, large current causes heat and fire - current blows the fuse and cuts off the mains electricity supply

52
Q

What are circuit breakers

A

Can be used as an alternative to fuses

They detect a change in the current and safely switch off the supply - once fault is fixed, it can switched on agasin, doesn’t need replacing

Works very quickly, a fuse takes some time to melt and won’t prevent you getting a shock eg if you touch a live wire

Physics (13 decks)

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