Energy power and resistance Flashcards
What is an ideal voltmeter?
Infinite resistance so no current can pass through
Is potential difference when work is done or from charge carriers?
Work is done by charge carrier- they lose energy as they pass through a component.
What is electromotive force?
When charge particles chain energy from a battery.
Define resistance?
The ration between v and I.
What is ohm’s law?
For a metallic conductor p kept at constant temperature,
Current is directly proportional to voltage.
What is a diode?
Allows current to follow in one particle direction.
How does a thermistor work?
Increase in temperature = decrease in resistance.
- initially the charge carriers are locked within a material and then when the temperature gets hotter the electrons are free and can move around and transfer charge.
In dark conditions what is resistance of LDR?
High resistance as the number density of free electrons is low
In light conditions what is the resistance of LDR?
Reistance is low and so the number density of free electrons is high.
What is electrical energy?
E=pt
Measure in joules or kWh
What is electrical power?
P=W/t
Measured in watts
Define electrical power?
Rate of energy transfer
Define a kilowatt hour
The energy transferred by and electrical device with a power of 1 kw operating for a time of 1 hour.
Define potential difference.
The energy transferred from electrical energy to other forms per unit charge.
What is 1000v equal tov
1000j of energy transferred per unit charge.
What does work for potential difference?
Work is done by charge carriers
“Energy is transferred” by charge carriers
What does work for emf?
Work is done on charge carriers
“Energy is transferred to charge carriers”
Emf is used when charged particles…. From a power source
Gain energy
Define emf
The energy transferred from chemical energy to electrical energy per unit charge.
What happens when temperature of a wire increases?
The positive ions vibrate more and so more frequent collisions occur between the charge carriers and positive ions so the charge carriers do work more( transfer energy) more
What is the resistivity of a good conductor?
Relatively low
10-8
Why does voltmeter reading stay constant when a battery has no internal resistance?
Voltage isnt “lost” so the full voltage would be shown
State a similarity of pd and emf
Same unit
State difference in pd and emf:
Emf:
Energy is transformed to electrical
Charge gains energy
Work done on charges
Pd:
Energy is transferred to other forms eg heat
Charge loses energy
Work done by charges
