1
Q
What is the current in parallel circuits?
A
- the total current flowing around the circuit is equal to the total of all currents through the separate component
- in a paraelle circuit, there are junctions where the current splits or rejoins. the total current going into a junction has to equal the total current leaving
- if two identical components are connected in parallel, then the same current will flow through each component
2
Q
How does increasing the voltage work to distribute energy?
A
- step-up transformer steps up the voltage, for efficient transmission and brings it down to safe, usable levels at the step-down transformer
- voltage is increased using a step-up transformer
- step-down transformers brings voltage down
3
Q
Label the three wires on a plug
A
left: neutral wire (blue)
middle: earth wire (green and yellow)
right: live wire (brown)
4
Q
Why do diodes rectify alternating current?
A
- mains electricity supplies alternating current
- many devices need direct current
- a single diode only lets through current in half of the cycle
- called half wave rectification
5
Q
What is a light-dependent resistor?
A
- a reistor dependent on the intensity of light
- in bright light, resistance falls
- in darkness, resistance is highest
6
Q
What is charge?
A
- the size of the electric current is the rate of flow of electric charge
7
Q
What is a thermistor?
A
- a temperature dependent resistor
- in hot conditions, resistance drops
- in cool condition, resistance increases
8
Q
What is the blue wire?
A
- the NEUTRAL wire
- is always at 0V
9
Q
What are series circuits?
A
- the different components are connected in a line, end to end between the positive and negative of the power supply
- except voltmeters, but they’re not part of the circuit
- if you rremove or disconnect one component, the circuit is broken and they all stop
- not handy
10
Q
What is the current in series circuits?
A
- the same everywhere
- the size of current is determined by the total PD and the total resistance
11
Q
What reading do you get on an oscilloscope trace for DC and AC?
A
- DC: a straight line, due to same voltage
- AC: a repeating wave. you can work out the period and the frequency of the supply
12
Q
What is the formula for energy transformed
A
- energy transformed = charge x potential difference
13
Q
Circuit Symbols
A
GO LEARN THEM NOW!
14
Q
What happens if you increase the resistance of a variable resistor?
A
- decreases the current flowing through the circuit
15
Q
What is a diode?
A
- a device made from a semiconductor material such as silicon
- used to regulate the potential difference in circuits
- lets the current flow freely thorugh it in one direction, but not in the other (very high resistance)
16
Q
What is the equation for charge, current and time?
A
- current (A) = charge (Q) / time (s)
17
Q
What is the cell voltage in series circuits?
A
- they add up
18
Q
What is the formula for electrical power?
A
- power = current x potential difference
- P = I x V
19
Q
Learn the current-potential difference (I-V) graphs
A
LEARN THEM NOW!
20
Q
What is the resistance in series circuits?
A
- total resistance is the sum of all resistance
- the bigger the resistance of the component, the bigger its share of the total PD
21
Q
What is current?
A
- a flow of electric charge round a circuit
- in amperes A
- current will only flow through a component if there is a potential difference across that component
22
Q
What does anything that supplies electricity also supply?
A
- energy
23
Q
how does the National Grid work?
A
- takes electrical energy from the power stations to where its needed in homes and industry
- it enable power to be generated anywhere on the grid and supplied anywhere else on the grid
24
Q
What current do cells and batteries supply?
A
- DC
- current always flowing in the same direction
25
What is the ammeter?
- measure the current (in amps) flowing through the component
- must be placed in series
- can be put anywhwere in series in the main circuit but never parallel
26
What is a kilowatt hour?
- the amount of electrical energy used by a 1kW appliance left on for 1 hour
27
How should fuses be rated?
- rated as near as possible but
| - just higher than the normal operating current
28
What is the power of an appliance?
- the rate at which it transfers energy
29
What is the main reason why mains electricity is AC?
- so that transformers work
| - they only work on AC
30
What are circuit breakers?
- an electrical safety device used in some circuits
- they protect the circuit from damage if too much current flows
- when they detect a surge in current, they break the circuit by opening a switch
31
Describe safety features in a three pin plug
- cable grip tightly fastened over the cable outer layer
- metals parts made of copper or brass as they are good conductors
- case, gable grip and cable insulation made of rubber and plastic because good insulators and flexible
32
Why does fuse rating increase?
- the larger the current, the thicker the cable
| - the thicker the cable, the larger the fuse
33
What are the pros and cons of circuit breakers?
- you can reset it easily by flicking a switch, so convenient
- operates much faster
- safer, no need to melt fuse
- work for small current changes, so more effective than fuses
- a lot more expensive
34
What is the problem with a high current when distributing electricity?
- you lose a lot of energy through heat in the cables
| - cheaper to increase the voltage
35
What is the voltmeter?
- measures the potential difference (in volts) across the component
- must be placed in parallel around the component
- a voltmeter has a very high resistance so if you place it in series in the circuit, there will be almost no current able to flow
36
What is the formula for resistance, potential difference and current?
potential difference (V) = current (I) x resistance (R)
37
Describe the residual current circuit breaker (RCCB)
- if live wire is touched, a small but deadly current will flow through them to the earth
- this means the neutral wire carries less current than than live wire
- RCCB detects this difference and cuts off power by opening a switch
38
What is potential difference?
- the driving force that pushes the current round
- also called voltage V
- it is the energy transferred per coulomb of charge that passes between two points in an electrical circuit
39
What do resistors produce when current flows through them?
- heat
| - the more current that flows, the more heat is produced
40
Give the equation for power rating
- power (W) = energy transferred (in J) / time (s)
41
What is the green and yellow wire?
- the EARTH WIRE
- protects the wiring and for safety
- it works with a fuse to prevent fire and shocks
- attached to the metal casing of the appliance and carries the electricity to earth if something goes wrong and the live and neutral wires touch the metal case
42
What is the potential difference in parallel circuits?
- all components get the full source of PD, so voltage is the same across all components
- e.g. identical bulbs in parallel will be at the same brightness
43
what is double insulation?
- if an appliance has a plastic casing and no metal parts showing
- so it doesnt need an earth wire
- these are two-core cables
44
Describe how earthing and fuses prevent electrical overloads
- if a fault develops in which the live wire touches the metal case, then because the case is earthed, too great a current flows in through the live wire, through the case and out down the earth wire
- this surge in current melts the fuse when the amount of current is greater than the fuse rating
- this cuts off the live supply and breaks the circuit
- this isolates the whole appliance, making it impossible to get an electric shock from the case also prevents risk of fire caused by heating effect
45
What happens when resistor gets hot?
- when an electrical charge flows through a resistor, some of the electrical energy is transferred to heat energy
- resistor gets hot
- this energy causes the ions in the resistor to vibrate more
- its more difficult for the charge-carrying electrons to get through the resistor
- current can't flow as easily and resistance increases
46
What is the formula for potential difference?
- PD (V) = energy transferred (E) / Charge (Q)
47
What is the potential difference in a series circuit?
- the total PD is shared between various components
| - the voltages round a series circuit always add up to the source voltage
48
What happens to the charge when a bigger current flows?
- a bigger charge
49
What happens when an electrical charge foes through a charge in potential difference?
- energy is transferred
50
What are parallel circuits?
- each component is separately connected to the positive and negative of the supply
- if you remove or disconnect one, it will hardly affect others
51
Descrive UK mains supply
- AC supply, current constantly changing direction
- approx 230 volts
- frequency is 50 cycles per second (50 Hz)
52
Which wires does electricity normally flow through?
- neutral and live wire
53
What is resistance?
- anything in the circuit that slows the flow down
| - in ohms
54
What are light-emitting diodes?
- an Led emits light when a current flows through it in the forward direction
- used a lot in lighting as they used a much smaller current
55
What is the brown wire?
- the LIVE wire
| - alternates between high positive and negative voltage
56
The ______ the resistance of a component, the smaller the current that flows?
- greater
IGCSE Physics
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