Current Electricity Flashcards
Only when will charge flow around a circuit
When it’s closed at there is a potential difference
The greater the resistance…
The smaller the current
When is the current directly proportional to the p.d in an ohmic conductor
When the temp is constant
For an LDR what happens to the resistance in 1, bright light 2, dark light
1, decreases
2, increases
For a thermistor what happens to resistance when it is 1, hot 2, cold
1, the resistance drops
2, the resistance increases
What happens to the overall resistance when u add more resistors in a parallel circuit
It decreases as you add more
What happens to the overall resistance when u add more resistors in a series circuit
The resistance increases
What is the equation linking charge, current and time
Charge= Current x Time
Q=It
Which wires create more resistance, short wires or long wires
Longer wires
Why is resistance greater at higher temperatures for metals
Because the flow of electrons is disturbed by the vibration of the metal atoms
How is potential difference measured in a series circuit
The total potential difference is shared between the components
Total p.d around a series circuit adds up to the source
Vt=V1+V2+V3
How is potential difference measured in a parallel circuit
All components get the full source p.d
Each branch had the same p.d as the power supply
Vt=V1+V2+V3
How is current measured in a series circuit
Current is the same at any point in the circuit
It= I1=I2=I3
How is current measured in a parallel circuit
Current in the branches adds up to the total current leaving the cell
It=I1+I2=I3
What is an LDR
A special type of resistor that is dependant on the intensity of light
In darkness the resistance is high
In brightness the resistance is low
How is resistance measured in a series circuit
The sum of all the resistance
Rt=R1+R2+R3
How is resistance measured in a parallel circuit
The total resistance in a parallel circuit
1/Rt=1/R1+1/R2+1/R3
How to calculate resistance
R=V/I
What is ohm’s law
The current through an ohmic conductor is directly proportional to the p.d across is as long as temp and other physical factors are constant
What is the IV characteristics of an ohmic conductor
A straight line
What is the IV characteristic of filament lamps,Why
Curved line
When charge flows through lamps some energy is transferred to surroundings as thermal energy
Resistance increases with temp, as particles have more energy so vibrate more, meaning it’s harder for electrons to flow
What is the IV characteristic of a diode, why
Flat line up to a point where no current can flow
When direction of current is reversed there will be a very high resistance
How to measure the resistance of a wire
Set up a circuit, with ammeter in series with a meter ruler, voltmeter in parallel with the ruler
Attach a crocodile clip to the wire at 0cm position
Attach another crocodile clip which will be moved throughout the test to investigate resistance at different lengths
Once the circuit is set up, begin the experiment by turning on the power pack, making sure it has a fixed reading throughout, recording the current and pd
Turn off the power, so that the wire doesn’t overheat, whilst you adjust the length of the wire
Once you have a good amount of data(10-100cm) calculate resistance using R=V/I
Plot a graph with resistance on the y axis and wire length on the x
Will a thinner or thicker wire have more resistance
Thinner wire because the electrons from the charge flow will collide with more atoms in the wire
