electricity Flashcards
What is a fixed resistor?
ohmic conductor,has a resistance that does not change.
What is a resistor?
restricts/ limits the flow of electrical current.
What is a variable resistor?
used in some dimmer switches/ volume controls
What is a direct current’?
movement of charge in one direction only.
What is an alternating current?
regularly changes its direction/ size
Calculation for charge.
current x time= Q= I x t
What is potential difference?
measure of energy.
Calculation for PD, energy, charge
energy/ charge= V= E/Q
What is current x resistance?
PD= V= I x R
Series calculations.
I1= I2= I3, PD of series= Vs= V1 + V2, Res. of series= Rtotal= R1+ R2
What is a series?
components are connected together, in one loop.
Parallel calculations.
I1= I2 + I4 =I3, PD of parallel= Vs= V1= V2, Res. in parallel= supply current divided between them
What is a parallel?
components connected alongside, extra loops.
Energy calculation.
power / time= E= P x t
What does the live wire do (brown)?
This carries the ac potential difference from the power supply. The potential difference between the live wire and the earth wire is about 230 V.
What does the neutral wire do (blue)?
This completes the circuit. It is at, or close to, the same potential as the earth wire (0V)
What does the earth wire do ( green and yellow stripes) ?
This is a safety wire. It is at 0V potential. It carries current only if fault happens in the circuit, to stop the appliance operating.
What is needed for a charge to flow
circuit must be closed, there must be a source of PD
What is a current?
flow of electrical charge
What is Q=It
Q= charge flow in coulombs C, I= current in amperes A, t= time in seconds
What is V=IR
V= PD in volts, I= current in amperes A, R= resistance in ohms
The greater the resistance of a component the …. the current for a given PD
smaller
If the resistance is constant what is the relationship between PD and current
directly proportional, linear graph
How does the resistance change with current?
Current increases -> electrons have more energy -> electrons flow through resistor ->collide with atoms in resistor -> trasnfers energy to atoms -> more vibrations -> difficult to flow through resistor-> decrease in current, increase in resistance
How does resistance change with temperature?
Hotter temperature resistance is low, as atoms vibrate when hot.
How does resistance change with length?
Higher resistance, lower current -> longer for atoms to travel
How does resistance change with light
The greater the light intensity, the lower the resistance
symbol for current
I
symbol for charge
Q
symbol for time
t
symbol for amps
A
symbol for coulombs
C
symbol for seconds
s
unit of current, I
amps, A
unit for charge, Q
coulombs, C
unit for time, t
seconds, s
what is the job of an ammeter
measures the current
a higher energy per coulomb of charge means…
higher potential difference, therefore a lighter bulb
what does the voltmeter measure
potential difference
how is the voltmeter connected
parallel
What is power
how much energy is transferred
calculation involving power, energy, time
power= energy/time
why does potential difference vary in a series circuit
shared, equal to total pd of battery
does the resistance of ohmic conductors change with the current
no- at a constant temperature current is directly proportional to PD
investigating resistance practical
1.attach crocodile clip to wire level 0cm on the ruler
2.attach second crocodile clip to wire, eg. 10cm away from first clip, write down length of wire between these clips
3.close the switch then record current and pd through wire
4.open switch then move 2nd crocodile clip along the wire. close switch again, record new lenght, pd, current
5. repeat this for a number of different lengths of the test wire
6.use measurements of current/pd to calculate resistance for each length of wire, R= V/I
7.Plot graph of resistance against wire length and draw line of best fit
components of I-V characteristic investigation
- set up test circuit
2.begin to vary variable resistor.
3.take readings from ammeter (current) and voltmeter(potential difference)
4.repeat twice to get average
5.swap over wires so direction of current is reversed
6.plot graph of current against voltage
what are the I-V characteristics of an ohmic conductor
the current at a constant temperature is directly proportional to the potential difference
what are the I-V characteristics of an filament lamp
the current increase, so does the temperature of lamp, so does resistance
what are the I-V characteristics of an diode
current will only flow through a diode in one direction, has a very high resistance in other direction
what is a I-V characteristic
a graph that shows how the current flowing through a component changes as the potential difference across it varies
