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GCSE Physics > Electricity > Flashcards

Electricity Flashcards

1
Q

In order for electric charge to flow through a closed circuit, what must the circuit include?

A

A source of potential difference.

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2
Q

What is electric current?

A

Electric current is the flow of electric charge (aka flow of electrons through a conductor). The (size of the) electric current is the RATE OF FLOW OF CHARGE.

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3
Q

What is the equation for electric current?

A

current (A) = charge (C) / time (s) -units
charge (Q) = current (I) x time (t) - quantities

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4
Q

How does current flow in a circuit?

A

The battery in the circuit gives energy to the electrons and pushes them around the circuit, from the negative terminal of the cell, round the circuit and back to the positive terminal of the cell.

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5
Q

What is conventional current?

A

The ‘conventional direction of current’ is from the positive terminal to the negative terminal (even though it’s actually the other way round).

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6
Q

What is potential difference?

A

Potential difference of a battery is a measure of the energy given to a unit of charge passing through the battery OR
Potential difference is how much electrical energy a unit of charge transfers to an electrical component.

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7
Q

What is the equation for potential difference?

A

potential difference = energy / charge
(V = E/Q)

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8
Q

What two things does current depend on?

A

The current through a component is dependent on both the resistance of the component and the potential difference across the component. The greater the resistance of the component the smaller the current for the given potential difference across the component.

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9
Q

What is the equation that links potential difference, current, and resistance?

A

potential difference = current x resistance
V = IR

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10
Q

Required practical 3

A
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11
Q

What does Ohm’s law state?

A

Ohm’s law states that the Current (I) through a resistor (R) at a constant temperature is directly proportional to the potential difference (V) across the resistor.

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12
Q

How does Ohm’s law apply to an ohmic conductor?

A

A conductor that obeys Ohm’s law is called an ohmic conductor.
In an ohmic conductor, the current (at a constant temperature) is directly proportional to the potential difference across the resistor. This means that resistance remains constant as the current changes.

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13
Q

Describe the graph of an ohmic conductor.

A

I on y-axis, V on x-axis. It is a straight line through the origin. The value of resistance R in this graph is 1/gradient.Wh

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14
Q

What components do not obey Ohm’s law? What happens instead?

A

The resistance of components such as lamps, diodes, thermistors and LDRs is not constant; it changes with the current through the component.

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15
Q

What happens to the temperature of a filament lamp as the resistance increases? What would a graph of this look like?

A

As the temperature of the filament lamp increases, the resistance of the filament lamp also increases. The graph would look like an ‘s’ shape through the origin. (So, when resistance is high, current is low, and potential difference is high, and when resistance is low, current is high, and potential difference is low)

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16
Q

What happens to the current and resistance in a diode?

A

Current only flows in one direction. The diode has a very high resistance in the reverse direction. (looks like a backwards L shape).

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17
Q

As temperature increases, what happens to the resistance of a thermistor?

A

As the temperature increases, the resistance of a thermistor decreases.

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18
Q

Explain why the potential difference across a thermistor changes as the temperature in the house decreases.

A

As the temperature in the house decreases, the resistance in the thermistor increases, therefore potential difference also increases because they are directly proportional.

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19
Q

When the temperature of resistor X increases, its resistance increases. What happens to the potential difference across X, current in X, and total current in the circuit if temperature increases?

A

Potential difference across X would stay the same. Current in X would decrease, and total current in the circuit would decrease. (Because pd remains constant and V= IR).

20
Q

As light intensity increases, what happens to the resistance of an LDR?

A

As light intensity increases, resistance of an LDR decreases.

21
Q

Required practical 4

A
22
Q

What are the two ways of joining electrical compononents?

A

Series and parallel circuits

23
Q

What is a series circuit and what are its rules?

A

The components are connected one after another, in series.
They make a single, simple loop for the current to flow around.
If one bulb is broken, the whole circuit stops working.
There is the same current through each component. I1 = I2 = I3 etc.
The total potential difference of the power supply is shared between the components. Vtotal = V1 + V2 etc.
The total resistance of two components is the sum of the resistance of each component. Rtotal = R1 + R2

24
Q

What is a parallel circuit and what are its rules?

A

The components are connected in parallel with each other.
The current has a choice of routes (paths).
If one bulb is broken, there is still an uninterrupted path through the second bulb, so the second bulb stays lit.
The total current of the whole circuit is the sum of the currents through the separate components.
The potential difference across each component is the same.
The total resistance of two resistors is less than the resistance of the smallest individual resistor.

25
Q

What is mains electricity like in the UK? (Think frequency, power, and type of current)

A

Mains electricity in the UK is ac supply (alternating current). The electricity supply has a frequency of 50 Hz and is about 230 V.

26
Q

What are the three wires in the UK three-pin plug and what are their colours?

A

The live wire carries the alternating potential difference from the supply. It is brown.
The neutral wire completes the circuit. It is blue.
The earth wire is a safety wire to stop the appliance becoming live. It is literally connected to the earth. It has green and yellow stripes.

27
Q

What are the voltages of the different wires in the UK plug?

A

The potential difference between the live wire and the earth wire is 230V. The neutral wire, is at or close to 0V (earth potential). The earth wire is at 0V, and it only carries a current if there is a fault.

28
Q

A coffee machine has a metal case. Why would it me dangerous for the live wire of the electric cable to touch the metal case?

A

The metal case becomes live (has current flowing through it) which could lead to electrocution if someone touches it.

29
Q

Why is copper used for the wires and why is it coated in plastic?

A

Copper wires are good conductors. Plastic is a good insulator. Copper and brass resist corrosion and are good electrical conductors. copper is a better conductor than brass, and it is used for electrical wiring. Brass is stronger than copper, so it is used for the pins in electrical plugs.

30
Q

Why do some plugs not have an earth wire?

A

Because they have double insulation instead - they have plastic/wooden cases that don’t conducted.

31
Q

What is a fuse?

A

A fuse is a piece of wire that will melt if current over a certain size flows through it.

32
Q

How does a fuse work?

A

If too much current flows, the wire inside the fuse melts and this breaks the circuit, stopping the current from flowing.

33
Q

What are the two equations for power?

A

power = potential difference x current
power = (current)^2 x resistance
P = IV
P = I^2R

34
Q

What are the two equations for energy transferred?

A

energy transferred = power x time
energy transferred = charge flow x potential difference

35
Q

What is the National Grid? What does it do?

A

The National Grid is a system of cables and transformers linking power stations to consumers. Electric power is transferred from power stations to consumers via the National Grid.

36
Q

What are step-up and step-down transformers used for?

A

Step-up transformers are used to increase the potential difference from the power station to the transmission cables then step-down transformers are used to decrease, to a much lower value, the potential difference for domestic use.

37
Q

What is static electricity?

A

Static electricity is the result of an imbalance between negative and positive charges in an object. These charges can build up on the surface of an object until they find a way to be released or charged.

38
Q

How does charging by friction work?

A

When insulating materials rub against each other, they may become electrically charged. Negatively charged electrons are rubbed off one material and onto the other.

39
Q

Explain what happens to polythene rods and Perspex rods when they are charged.

A

Polythene rod gains electrons - becomes negatively charged.
Perspex rod loses electrons - has now more protons than electrons and becomes positively charged.

40
Q

What is charging by induction?

A

Bringing the negatively charged balloon near to the wall causes the electrons in the balloon to repel the electrons in the wall from the balloon.
This is called an induced charge separation - the surface wall is charged by induction. Induced charge separation leaves a positive charge on the surface of the wall closest to the balloon. Therefore the negatively charged balloon is attracted to the positively charged surface of the wall.

41
Q

How is a spark caused?

A

A sphere has a negative static charge; the electrons repel each other.
If you bring an earthed wire near to this charged sphere, the electrons “see” a nearby path towards spreading out.
Their negative presence repels electrons in the nearby end of the wire, leaving an induced positive charge.
The forces can get so large that the electrons on the surface of the sphere actually leave the surface and accelerate towards the earthed wire.
An electric current starts to flow through the air.
It makes the air so hat that it glows - spark.
Can ignite nearby flammable materials.

42
Q

True or false - all charged objects have an electric field.

A

True

43
Q

What is the relationship between the electric field strength of an object and the distance from it?

A

The electric field strength E decreases MORE RAPIDLY than the distance r from the charge increases.
Strength of electric field is inversely proportional to the square of the distance between the charges.
E & 1/r^2

44
Q

What happens if you put a charged particle in an electric field?

A

If you put another charged particle in an electric field, it will experience a force because it is in the field.

45
Q

What is the direction of the field for a positive and negative electric field. What is the direction of the force for each of them?

A

Electric field due to positive charge - direction of field is outwards. Direction of force is outwards.
Electric field due to negative charge- direction of field is inwards. Direction of force is inwards.

46
Q

How is an electric field casued?

A

There is an electric field DUE to a positive or negative charge. (not a positive or negative field)

GCSE Physics (6 decks)

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