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Electricity Flashcards

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2
Q

What are the two types of electrical charge

A

positive and negative charge

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3
Q

What are objects with no electrical charge called

A

Neutral

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4
Q

Like charges____
opposite charges ______

A

Like charges will replell each other
Opposite charges attract each other

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5
Q

Describe an atom

A

The atom is made up of a central part called the nucleus, containing protons which are positively charged, and neutrons which have no charge. It is sorrounded by orbiting Electrons which are negatively charged.

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6
Q

What happens in an atoms when electricity flows

A

The electrons move

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7
Q

What are conductors

A

Conductors are materials which allow electrical current to pass through them

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8
Q

What are insulators

A

Insulators are materials that don’t allow electrical current to pass through them.

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9
Q

Name 3 conductors

A

Any metal: i.e.
Gold
Iron
Copper

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10
Q

Name 3 insulators

A

Glass
Air
Plastic
Rubber
Wood

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11
Q

What is electrical current

A

Electrical current is defined as the electric charge transferred per unit time (per second)

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12
Q

What is the formula for charge

A

Q = It
Q= charge measured in coulombs (C)
I = current measured in amps (A)
t = time measured in seconds (s)

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13
Q

Describe electrical fields

A

Charged particles have electrical fields around them. these electrical fields apply a force to charged particles. This force can make the particle move. The path it follows depends on teh electrical field

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14
Q

What is the radial field.

A

The electrical field around a point charge. The arrows on the field lines show what would happen if a positive test charge was placed in the field.

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15
Q

What is the function of a cell

A

To provide voltage

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16
Q

What is the function of a battery

A

To provide voltage

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17
Q

What is the function of a lamp

A

To produce light

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18
Q

What is the function of a switch

A

To control a circuit (on/off)

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19
Q

What is the function of a resistor

A

To control resistance (fixed)

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20
Q

What is the function of a variable resistor

A

To control resistance (variable)

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21
Q

What is the function of a voltmeter

A

to measure voltage

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22
Q

What is the function of an ammeter

A

to measure current

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23
Q

What is the function of a motor

A

to produce rotational motion

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24
Q

What is the function of a loud speaker

A

To produce sound

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25
Q

What is the function of a microphone

A

to convert sound energy into electrical energy

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26
Q

What are the 2 types of electrical current?

A

AC - Alternating current
DC - Direct current

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27
Q

Descrribe alternating current

A

In an AC circuit, the flow of electrons is ​
continually changing direction back and forth.​

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28
Q

What is an example of an alternating current supply

A

The mains power supply is an example ​
of an AC supply.

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29
Q

Describe direct current

A

In a DC circuit the electrons always flow in the same direction.

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30
Q

What is an example of direct current supply

A

Examples of DC supplies include batteries and cells.

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31
Q

What is the identifying feature of a series circuit

A

A series circuit has only one loop

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32
Q

How does current in a series circuit work

A

The current in a series circuit is the same at every point

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33
Q

What is the identifying feature of a parallel circuit

A

Parallel circuits are constructed by placing each component on its own branch.

(multiple branches)

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34
Q

How does current in a parallel circuit work?

A

The currents in each of the branches add up to the total current from the supply.

35
Q

What is Voltage (Potential Difference)

A

Voltage (also known as potential difference) is a measure of the electrical energy given to each Coulomb of charge in a circuit.

Voltage is measured in Volts (V) using a voltmeter.​

36
Q

How do you use a voltmeter

A

A voltmeter is connected in parallel across ​
the component being tested meaning the ​
circuit does not need to be broken to use ​
a voltmeter.

37
Q

How does voltage in a series circuit work?

A

The voltages across all of the components in the circuit add up to the supply voltage.

38
Q

How does voltage in a parallel circuit work

A

The voltages across each branch of a parallel circuit are the same as the voltage across the supply.

39
Q

What is the voltage of the mains supply in the UK

A

230V

40
Q

What is a fuse?

A

A fuse is a safety device designed to protect the flex of an appliance.

41
Q

What must a fuse do?

A

A fuse must allow a normal running current to flow but melt/blow when a higher current flows through it.

42
Q

What are the standard fuse sizes

A

3A, 5A and 13A

43
Q

What is the general rule for appliances

A

Under 700W use a 3A fuse
Over 1200W use a 13A fuse

44
Q

Describe resistance

A

Charge flowing through a wire doesn’t get it all its own way. Anything in a circuit - like bulbs and wires – will resist the current. The more it resists, the higher its resistance.

45
Q

What is resistance measured in?

A

Resistance is measured in Ohms (Ω)
Resistance is measured using an ohmmeter

46
Q

How do you find the total resistance in a series circuit?

A

Add up the resistances in the circuit.

47
Q

How do find the resistance in parallel circuits?

A

1/Rt = 1/R1 + 1/R2 + ….

48
Q

What does Ohm’s law state

A

Current in a resistor is dirrectly proportional to the potential difference across the resistor.

49
Q

Ohm’s law formula?

A

V = IR

where:
V = voltage measured in volts (V)
I = Current measured in amperes (A)
R = resistance measured in ohms (Ω)

50
Q

In a voltage current graph how can you find the resistance

A

Finding the gradient of the line.

51
Q

What is an ohmic conductor?

A

An ohmic conductor is a component that obeys Ohm’s law. A graph of potential difference against current (a voltage current graph) gives a straight line with a positive gradient. The steeper the gradient, the higher the resistance.

52
Q

What is a non ohmic conductor

A

A bulb is an example of a non ohmic conductor. its voltage current graph does not follow a straight lin. Instead it gives a curve with an increasing gradient. It shows that the resistance increase as the current increases.

53
Q

Deescribe a variable resistor

A

Variable resistors are components in which the resistance can be changed. ​

This is often done by moving the position of a slider or turning a dial.​

​
They are used in dimmer switches and volume controls.

54
Q

Describe a Light dependent resistor

A

Light dependent resistors (LDRs) will vary resistance with varying light levels. ​

As the light level increase, the resistance of the LDR will decrease.​

Light Up Resistance Down LURD

55
Q

Describe a thermistor

A

Thermistors will vary resistance with varying temperatures​

As the temperature increase, the resistance of the thermistor will decrease.​

  Temperature Up Resistance Down TURD
56
Q

What is an electronic circuit

A

Electronic circuits are electrical circuits that are used to do something.​

​

57
Q

What are the 3 main sections of an electronic circuit

A

Input –> Process —> Output

58
Q

What is a photovoltaic cell

A

A photovoltaic cell is often just called a solar cell. It converts light energy to electrical energy.

59
Q

What is the diode?

A

The diode is a device that only allows current to flow in one direction.

It will only work when the cathode (-) of the diode is connected to the cathode (-) terminal of the power supply (anode connected to anode)

60
Q

What is the LED

A

LED stands for Light Emitting Diode.​

Like a diode, it is a low current device. It is destroyed by high currents. This means we need to fit a series resistor to LEDs to reduce the current to a safe level.

61
Q

How do you workout the value of a resistor for a LED

A

Frist work out the voltage across the resistor, Vr = Vs - Vled (MAX)

The resistor will need to have a maximum of ____ volts and ____ amps through it. Use Ohms law to find resistance.

62
Q

What is a capacitor

A

A capacitor consists of two metal plates separated by an insulator. It’s a device which can store electric charge.

63
Q

What is the relay

A

The relay is a switch that is operated by a magnetic field.

When the first circuit is complete, the current in the coil causes it to become magnetised. This pulls shut the switch in the second circuit.

64
Q

Describe a potential divider

A

A potential divider is a way of ​
dividing up the voltage (potential) ​
from a supply. This means we can ​
get exactly the voltage we need to ​
operate a circuit.​

In a potential divider circuit, the voltage across a resistor is related to its resistance. The higher the resistance of a resistor, the higher the voltage across it.​

Because a potential divider circuit is a series circuit, the current passing through both resistors is the same.

65
Q

What are the two potential divider equations

A

V2 = (R2/R1+R2)Vs

V1/V2 = R1/R2

Where:
Vs = voltage across the supply​

V1 = voltage across resistor 1​

V2 = voltage across resistor 2

R1 = resistance of resistor 1​

R2 = resistance of resistor 2​

66
Q

What are tansistor circuits?

A

Transistors can be used as electronic switches in circuits.

67
Q

What are the 2 types of trnasistor circuits

A

NPN transistors
MOSFETs

68
Q

Describe NPN transistors

A

If a high enough voltage is applied to the base of the transistor, then current flows between the collector and emitter.​

The ‘switch-on’ voltage for an NPN transistor is about 0.7 V.​

​

Below 0.7 V, the transistor will be OFF​

Above 0.7 V, the transistor will be ON

69
Q

Why are variable resistors used in transistor circuits

A

Many switching circuits involving transistors have a variable resistor as one of the components in the potential divider.​
`
Adjusting the variable resistor allows you adjust when the circuit switches on and off.

70
Q

What does MOSFET stand for

A

Metal Oxide Semiconductor field transistors

71
Q

Describe MOSFETs

A

they are operate the same way as NPN transistors

They ‘switch on’ at a higher voltage – about 2 V. ​

They can handle bigger output current than NPN transistors, so can run bulbs and motors.

72
Q

What is power?

A

Power is a measure of the energy transferred per second.​

Electrical devices are labelled with their power ratings.

73
Q

What is the Power relationship

A

P = E/t

where:

P = power measured in watts (W)
E= energy measured in joules (J)
t = time measured in seconds (s)

74
Q

What is electrical power?

A

Electrical power is the rate at which electrical energy is transferred. ​

It depends on both the current and the potential difference (voltage).​

75
Q

What is the relations ship for electrical power

A

P = IV
where:
P = power measured in watts (W)
I = current measured in amperes (A)
V = Voltage measured in volts (V)

76
Q

What are the alternative power relations ships

A

P = I^2 R

P = V^2/R

77
Q

Describe how a fuse works

A

Plugs have fuses fitted in them. ​

If an appliance – like a TV – starts to draw too high a current, the thin wire in the fuse will melt and cut off the current. ​

This stops the flex from overheating and possibly causing a fire.

78
Q

How do we know what fuse to use?

A

We can use P= I V to work out which fuse to use by calculating the operating current of the appliance.

79
Q

What are input devices?

A

Input devices convert one form of energy into electrical energy. This allows an external signal to be converted into an electrical one for use in a circuit.

80
Q

What is an analogue system?

A

An analogue system has a signal which can exist in any state between its maximum and minimum value. It is often described as a wave.

81
Q

What is a digital system

A

A digital system is one in which the signal can only exist at one of two states, off and on, also often described as L and R.

82
Q

What is the formula for energy efficiency?

A

Energy efficiency =
useful energy out * 100/Total energy in

Physics (7 decks)

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