Electricity Flashcards
(42 cards)
1
Q
What is a fuse?
A
- A safety device which melts above a stated current
2
Q
What is a thermistor?
A
- Device that changes resistance based on temperature
- Increased temperature = reduced resistance
3
Q
What is electric current?
A
- The rate of flow of electric charge
- Q = It
- Measured in Amps (A)
4
Q
What is a cell?
A
- A power source for a circuit
5
Q
What is a resistor?
A
- An electrical device that resists the flow of electrical current
6
Q
What is a circuit diagram?
A
- Shows how components are connected together
7
Q
What is a battery?
A
- Consists of two or more cells connected together
8
Q
What is a diode?
A
- Device which only allows current to flow in one direction (direct current)
9
Q
What is a light emitting diode?
A
- A diode which emits light
10
Q
What is voltage?
A
- Energy transferred per coulomb of charge
- Measured in volts (V)
11
Q
What is resistance?
A
- V = IR
- Measured in ohms Ω
12
Q
A filament lamp’s resistance increases ___
A
if the filament’s temperature increases
13
Q
An LDR’s resistance decreases ___
A
if the light intensity on it increases
14
Q
For components in series:
A
- The current is the same ini each component
- The total voltage is shared between the components
- Adding the resistances gives the total resistance
15
Q
What happens if you add more resistors in series?
A
- Increase the total resistance
- Current reduces
- Total voltage remains unchanged
16
Q
What happens to resistance of components in parallel?
A
- Total resistance decreases as more components are added
- More paths for current to flow through
- Total current through the resistors increases
- Total resistance is always smaller than the smallest resistor
- Total voltage is unchanged
17
Q
For components in parallel:
A
- The total current is the sum of currents through the separate components
- The voltage across each component is the same
18
Q
The bigger the resistance of a component ___
A
the smaller the current that will pass through that component
19
Q
Relationship between resistance and length of wire
A
- Resistance is directly proportional to the length
20
Q
The IV graph for a resistor?
A
- V on x axis
- I on y axis
- Straight through the origin (directly proportional)
- Resistance is constant
21
Q
The IV graph for a filament lamp
A
- Current increases, resistance increases
- Stretched S shape with less accentuated curve
22
Q
The IV graph for a diode
A
- Forward resistance low after 0.6V
- Nothing on negative x axis, so along the x axis (y = 0)
- Suddenly shoots up after 0.6V
23
Q
Name the parts of a plug
A
- Neutral = blue
- Earth = green and yellow
- Live = brown and has the fuse
24
Q
What are the mains voltage?
A
- 230V
25
What is the voltage between the neutral and earth?
- 0V
- Anything else indicates a fault
26
Calculate power in an electric circuit
- P = IV
- P = E/t
- Measured in watts (W)
27
What is the national grid?
- A system of cables and transformers
- Links power stations to consumers
28
What is a step up transformer?
- Increases voltage and lowers current
29
What is a step down transformer?
- Decreases voltage and increases current
30
What is alternating current?
- An electric current that periodically reverses in direction in the circuit
31
What is Ohm's Law?
- The current flowing through a metal wire at constant temperature is proportional to the voltage across it
32
Using a fuse without an earth wire?
- If a fault occurs, someone might still get a shock if they touch the casing with a fault
- Fuse melts, breaking the circuit
33
Using an earth wire without a fuse?
- High current would flow to earth as soon as a fault occurs
- With no fuse, the high current might cause a fire instead of melting the fuse
34
Why is using a fuse and the earth wire the safest option?
- As soon as a fault occurs, high current would flow to earth, melting the fuse, breaking the circuit
35
How to choose a fuse?
- Work out the operating current of the device
- Choose the fuse closest in the value above the operating current
36
What is direct current?
- Only flows in one direction
37
What is charge?
- Can be positive or negative
- Measured in coulombs (C)
38
What is charging by friction?
- An object gains or loses electrons by rubbing
39
What is induced charge?
- When electrons move in an object leaving areas of positive and negative charge
- Net overall charge remains neutral
40
What are the uses of charge?
- Spray painting bikes
- Photocopiers
41
What are the dangers of charge?
- Refuelling of charge
- Danger of sparks
42
What is double insulation?
- Insulation around wires themselves
- Non-metallic case that acts as a second layer of insulation
