Unit 2 - Electrical Circuits Flashcards
What does a Voltmeter measure?
Measures voltage/potential difference (v/volts)
What does an ammeter do?
Measures current - in amperes (A)
How is an ammeter connected to the circuit?
It is always connected into the circuit
How is the voltmeter connected to the circuit?
It is connected across a component in parallel
What is the pd across all the cells equal to?
The sum of the pd’s across the bulbs in a series circuit
The current is the same whenever..?
..you measure it in a series circuit
What do more cells give the circuit?
- Bigger p.d
- Bigger current
- Brighter bulb
What does more bulbs give the circuit?
- Lower current
- Dimmer bulbs
- Pd per bulb decreases
What happens to all the bulbs in a series circuit if 1 goes out?
All the others also go out
What happens to the bulbs in a parallel curcuit if one goes out?
They stay lit
How many paths for the current in a seriews circuit?
Only 1
How many paths for the current in a parellel circuit?
More than 1
What is this?
A cell
What is this?
A battery
What is this?
An open switch
What is this?
A closed switch
What is this?
A filament lamp
What is this?
An Ammeter
What is this?
A Voltmeter
What is this?
LDR (light-dependant resistor)
What is this?
A diode
Whats this?
An LED (light emitting diode)
Whats this?
A fuse
Whats this?
A resistor
Whats this?
A variable resistor
Whats this?
A thermister
What is the current?
The rate of flow of charge
What is the potential difference?
The pd between 2 points in an electric circuit is the work done (energy transferred) per coulomb of charge that passes between the points
Resistance
A measure of how hard it is for a current to pass through any component
What is the total resistance in a circuit?
R1+R2 (resistors added together)
What is the total pd in a circuit?
the pd’s added together
When calculating the pd, if each cell =1.5V and the cells are facing the same way what is the total pd?
1.5+1.5 = 3V
When calculating the pd, if each cell =1.5V and the cells are facing opposite eachother what is the total pd?
1.5V-1.5V = 0V
Factors that effect resistance?
- Material
- Cross sectional area (thickness)
- Temperature
- Length
In terms of resistance - the longer the wire?
The more resistance
In terms of resistance - thinner wire =?
More resistant
In terms of resistance, the thicker the wire?
The lower the resistance
What does ohms law state?
The current through a fixed resistance will be proportional to the pd across the resistor providing the temoerature is constant
What is the equation for the resistace?
R = I/V
resistance = current / pd
Whats the equation for the gradient?
Rise
step
What is the use of a diode?
Only allows current to flow thorugh in one direction so it can be used to protect electronic circuits
Whats the difference between a conducting and unconducting diode?
Use of an LDR
Can be used to control circuits as light sensors/automatically switches light etc because its **resistances changes **as the **light intensity changes **
Use of a thermistor?
In central heating systems as part of the thermostat of any circuit to control temperature because its resistance varies with temperature
Whats the use of LED’s?
- In small scale lighting eg on electronic equipment
- In low power lighting in buildings
- **Brake lights ** because their long loved and very reliable
Static electricity: Two like charges..?
Repel
Static electricity: two unlike charges..?
Attract
Electrons (which are negative) can move from one ____?____ to another due to ?
From one insulator to another due to rubbing/friction
What happens if something looses electrons?
It becomes positively charged
What happens if something gains electrons?
It will bcome negatively charged
What is the frequency and voltage of the mains electricity we use?
Voltage - 230V
Frequency - 50Hz
What is an alertnating current?
An electric current that continually changes its direction
Whats a direct current?
An electric current that flows in the same direction at all times
What is another source of electricity we use thats not mains?
Batteries, these have no frequency and have a direct current
What happens when a current passes through a resistor?
Heat energy is produced
(it can be good though eg kettle, iron)
How is a point of high resistance caused?
By damage in a wire, it can cause overheating
Why are ovens etc connected by thick wires?
So that the large current doesnt cause overheating
What happens when a large current pases through a thin fuse wire?
The wire melts and breaks the circuits
Whats the equations for normal current?
Power
_________
Voltage
Whats a RCCB and how does it work
Residual current circuit breaker
it works by comparing the current in the live and neutral wires if the icrrents are different they break the circuits up
What are the advantages of an RCCB?
Resettable (less mistakes made by changing fuses manually)
Faster
