section 2: Electricity Flashcards

1
Q

the properties of a circuit:

A

-current is the flow of charge round the circuit, electrons carry the charge (-) and will only flow through a component if there is voltage across that component (unit: ampere- A)
-voltage (potential difference) is what drives the current round the circuit (unit: volts- V)
-resistance is anything in the circuit which slows the flow. If you add more components to the circuit there will be a higher overall resistance (unit: ohm)
-if you increase the voltage-then more current will flow
-if you increase the resistance-then less current will flow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

the ammeter + voltmeter:

A

the ammeter:
-measures the current flowing through the component
-must be placed in series anywhere in the main circuit, but never in parallel like the voltmeter
the voltmeter:
-measures the voltage across the component
-must be placed in parallel around the component under test-NOT around the variable resistor or the battery!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

ac & dc:

A

-the Uk mains electricity supply is approximately 230 volts
-it is an a.c supply (alternating current), which means the current is constantly changing direction
-cells and batteries supply d.c (direct current), which means that the current keeps flowing in the same direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Ohm’s Law: formula linking voltage, current and resistance

A

voltage = current x resistance
V = IR
- steeper line = lower the resistance
-a straight-line = constant + resistance
-graph curves = resistance is changing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

current-voltage graphs:

A

1) Wire: the current through a wire (at constant temperature) is proportional to voltage
2) Different (fixed) Resistors: the current through a resistor (at constant temperature) is proportional to voltage. Different resistors have different resistances, hence the different slopes
3) Metal Filament Lamp: as the temperature of the metal filament increases, the resistance increases, hence the curve
4) Diode: current will only flow through a diode in one direction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Light-Emitting Diodes: LEDs

A

-LEDs emit light when a current flows through them in the forward direction. They have lots of practical applications
-they are used for the numbers on digital clocks, in traffic lights and in remote controls
-unlike a light bulb, they don’t have a filament that can burn out
-LEDs, like lamps, indicate the presence of current in circuit. They are often used in appliances to show that they are switched on

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Light-Dependent Resistors: LDRs

A

-LDRs are a special type of resistor that changes its resistance depending on how much light falls on it
-in bright lights, the resistance falls and in darkness, the resistance is highest
-this makes it a useful device for various electronic circuits, e.g: burglar detectors
-in graphs the same + a non-ohmic resistor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

thermistors:

A

-a thermistor is a temperature-dependent resistor
-in hot conditions, the resistance drops and in cool conditions, the resistance goes up
-thermistors make useful temperature detectors, e.g: car engine temperature sensors, thermostats and fire alarms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

fixed resistors + wires: graph

A

-current through a fixed resistor or a wire increases as the p.d across it increases
-current is directly proportional to p.d for a fixed resistor (or a wire)
-this is because the resistance of the fixed resistor (or wire) stays constant
-current on y-axis and p.d on x-axis
-ohmic resistor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

filament lamps: graph

A

-current + voltage is not directly proportional because the resistance of the filament lamp increases as the temperature of the filament increases
-the higher temperature causes the atoms in the metal lattice of the filament to vibrate more
-this causes an increase in resistance as it becomes more difficult for free electrons (the current) to pass through
-resistance opposes the current, causing the current to increase at a slower rate
-non-ohmic resistor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

diodes:

A

-allows current in one direction only called: forward bias
-in the reverse direction, the diode has a very high resistance, and therefore no current flows called: reverse bias

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

diodes: IV graphs

A

-when the current is in the direction of the arrowhead current symbol, this is forward bias
-shown by a sharp increase in p.d and current on the right side of the graph
-when the diode is switched around, this is reverse bias
-shown by a zero reading of current or p.d on the left side of the graph
-non-ohmic resistor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

resistors:

A

-two types: fixed resistors, variable resistors
-fixed resistors have a resistance that remains constant
-variable resistors can change the resistance by changing the length of wire that makes up the circuit
-a longer length of wire has more resistance than a shorter length of wire

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

thermistors: graph

A

-the resistance changes a lot for small changes in temperature
-resistance decreases with increasing temperature
-non-ohmic resistor

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

series circuits: properties

A

-in series circuits, the different components are connected in a line, end to end, between the +ve and -ve of the power supply (except for voltmeters, which are always connected in parallel, but they don’t count as part of the circuit)
-if you remove or disconnect one component, the circuit is broken and they all stop working. This is generally not very handy, and in practice only a few things are connected in series, e.g: fairy lights

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

series circuits: actual circuit

A

-the current is the same everywhere. I1 = I2 = I3 = … The size of the current depends on the total potential difference and the total resistance of the circuit (I = Vtotal divided by Rtotal)
-the total resistance is the sum of the resistance of each component in the circuit- Rtotal = R1 + R2 + R3 + ….

17
Q

parallel circuits: properties

A

-in parallel circuits, each component is seperately connected to the +ve and -ve of the supply (except ammeters, which are always in series)
-if you remove or disconnect one component, it will hardly affect the others at all
-this is obviously how most things must be connected, for example in cars and in household electrics

18
Q

parallel circuits: actual circuit

A

-the potential difference is the same across all branches. V1 = V2 = V3 = etc
-current is shared between branches. Itotal = I1 + I2 + I3 + etc.
-there are junctions where the current either splits or rejoins. The total current going into a junction equal the total current leaving it, as charge can’t just dissapear or appear
-if two identical components are connected in parallel then the same current will flow through each component

19
Q

formula linking charge, current and time

A

charge = current x time
Q = It

20
Q

formula linking energy transferred, charge & voltage:

A

energy transferred = charge x voltage
E (in joules) = Q x V

21
Q

formula linking energy transferred, charge, current & resistance:

A

energy transferred = charge x current x resistance
E = Q x I x R

22
Q

wires in a plug:

A

-there are three wires in a plug-live,neutral and earth
-only the live and neutral wires are usually needed, but if something goes wrong, the earth wire stops you getting hurt
-live wire (brown): provides a path along ehich the electrical energy from the power station travels
-neutral wire (blue): completes the circuit by carrying the current back to the original power source
-earth wire (green + yellow): to protect the user by providing a path for the current to escape without passing you/user

23
Q

appliances being earthed and insulated:

A

-all apliances with metal cases must be “earthed” to reduce the danger of electric shock, “earthing” just means that the case must be attached to an earth wire, an earthed conductor can never become live
-if the appliance has a plastic casing and no metal parts showing then it’s said to be double insulated
-the plastic is an insulator, so it stops a current flowing-which means you can’t get a shock, anything with double insulation doesn’t need an earth wire-just a live and neutral

24
Q

circuit breakers:

A

-circuit breakers are an electrical safety device used in some circuits, like fuses, they protect the circuit from damage if too much current flows
-when circuit breakers detect a surge in current in a circuit, they break the circuit by opening a switch
-a circuit breaker can easily be reset by flicking a switch on the device, this make them more convenient than fuese-which have to be replaced once they’ve melted

25
Q

electrical power

A

-> electrical power is the rate at which an appliance transfers energy
-an appliance with a high power rating transfers a lot of energy in a short time
-this energy comes from the current flowing through it. This means that an appliance with a high power rating will draw a large current from the supply
electrical power (measured in Watts) = current x voltage
P=IV

26
Q

formula linking energy transferred, current, voltage and time

A

Energy transferred = Current x voltage x time
E = I x V x t