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Electricity Flashcards

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1
Q

What is electric current?

A

It is the flow of electrical charge-greater flow = higher current.

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2
Q

How is an ammeter and voltmeter connected?

A

An ammeter is connected in series. A voltmeter is connected in parallel to the component.

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3
Q

Charge flow equation.

A

Charge flow = Current * time Q=It

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4
Q

What is the resistance of a component?

A

The resistance of a component is the measure of how it resists the flow of charge.

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5
Q

What happens when you increase resistance and voltage?

A

Increasing resistance reduces the current.
Increasing the voltage increases the current.

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6
Q

What does potential difference tell us?

A

It tells us the difference in electrical potential from one point in a circuit to another.

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7
Q

Potential difference equation.

A

Potential difference = current * resistance V=IR

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8
Q

(RP) Investigate the factors that affect the resistance of an electrical component.

A

1) Set up the circuit.
2) Pre-test the circuit and adjust the supply voltage to ensure that there is a difference in the readings taken at the highest and lowest temp.
3) Record the voltage and current at a range of lengths, using crocodile clips. to grip the wire.
4) Use the variable resistor to keep the current through the wire the same at each length.
5) Use the voltage and current measurements to calculate resistance.

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9
Q

what are the variables for the required practical: Investigate the factors that affect the resistance of an electrical component.

A

IV= The length of the wire
DV= the voltage.
CV= The current (kept the same to prevent the wire from getting too hot and the resistance from changing).

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10
Q

What are current graphs (V-I graphs) used to show?

A

They are used to show the relationship between the potential difference and current for any component.

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11
Q

What do the different current graphs show?

A

A straight line through the origin indicates its directly proportional (current and pd).
A steep gradient indicates low resistance as a large current will flow for a small pd.
A shallow gradient indicates high resistance as a large pd difference is needed to produce a small current.
For some resistors the value of R is not constant but changes as the current changes, this results in a non-linear graph.

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12
Q

(RP) Investigate the V-I characteristics of a filament lamp, a diode and a resistor at constant temperature.

A

1) Set up the standard test circuit.
2) Use the variable resistor to adjust the potential difference across the test component.
3) Measure the voltage and current for a range of voltage values.
4) Repeat the experiment at least three times to be able to calculate a mean.
5) Repeat for the other components to be tested.

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13
Q

What are the variables of the RP Investigate the V-I characteristics of a filament lamp, a diode and a resistor at constant temperature?

A

IV= The potential difference across the component (set by the variable resistor.
DV= The current through the component, measured by the ammeter.

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14
Q

What is an ohmic conductor?

A

An ohmic conductor is a resistor in which the current is directly proportional to the pd at a constant temperature.
-This means that the resistance remains constant as the current changes.
-Indicated by a linear graph.

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15
Q

Filament lamps.

A

-As the current through a filament lamp increase, its temperature increases.
-This causes the resistance to increase as the current increase
-Indicated by a curved graph.

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16
Q

Diodes.

A

-The current through a diode will only flow in one direction.
- The diode has a very high resistance in the reverse direction.
-Indicated by a horizontal line along the x-axis which shows that no current flows.

17
Q

Thermistors.

A

-The resistance of a thermistor decreases as the temperature increases.
-Makes them useful in circuits where temperature control or response is required.
-

18
Q

Light Dependent Resistors (LDRs)

A

-The resistance of an LDR decreases as light intensity increases.
-This makes them useful where automatic light control or detection is needed eg street lights.

19
Q

What are the power equations?

A

Power= potential difference * current
power= (current)2 * resistance

20
Q

Direct current.

A

-Has a potential difference that is always positive or always negative-current direction is always constant..
-Supplied by batteries or cells.

21
Q

Alternating current.

A

-Has a potential difference that alternates from positive to negative- the current direction alternates.
- Type of current used in mains electricity.

22
Q

What is the mains electricity in the uk?

A

230V. Frequency of 50Hz

23
Q

What are the 3 wires in a plug?

A

Live wire- (brown) 230V
Earth wire- (green and yellow) 0V
Neutral wire- (blue) 0V

24
Q

How does current flow in a plug?

A

-The pd causes current to flow through the live wire and neutral wire.
-The live wire carries the alternating potential from the supply.
-The neutral wire completes the circuit.
-Current will only flow in the earth wire if there is a fault connecting it to a non-zero potential.

25
Q

What is power?

A

Power is the rate at which energy is transferred or work is done.

26
Q

p=e/t

A

Power= energy transferred/time

27
Q

p=w/t

A

power=work done/time

28
Q

What are the 2 efficiency equations?

A

Efficiency= useful energy transfer/total energy transfer.
Efficiency= useful power output/total power input.

29
Q

What is the national grid?

A

A system of cables and transformers linking power stations to homes and businesses.

30
Q

E=QV

A

Energy transferred = current flow * potential difference.

31
Q

What happens at the power station?

A

The power station transfers the energy supply into electrical energy.

32
Q

Step-up transformers.

A

-The transformers increase the potential difference from the power station to the transmission cables.
-This reduces the current and therefore reduces the heating effect caused by the current.
Reducing heat= reducing energy loss so it makes the transmission more efficient.

33
Q

Step-down transformers.

A

-The transformers reduce the potential difference from the transmission cables to a much lower value for domestic use.

34
Q

What happens when friction moves negatively charged electrons from one material to another?

A

-The object that gains electrons becomes negatively charged.
-The object that loses electrons becomes positively charged.

35
Q

What is an isolated object?

A

An object that has no conducting path to earth.

36
Q

What kind of force is an electrostatic force?

A

Non-contact.

37
Q

What 2 factors does the strength of an electric field depend on?

A

-The distance from the object-the further away from the object, the weaker the field.
-The amount of charge- the higher the charge, the stronger the field.

Physics (9 decks)

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