3 - Electricity Flashcards
Define current
Rate of movement of charge
Define potential difference
Energy per unit charged
Define emf
Total supply of voltage
Define power
Rate of energy transfer
Define resistance
Slows down flow of charge
Define internal resistance
Resistance due to power supply
Define efficiency
What proportion of energy is useful out of total energy
Define charge carrier density
Number of free electrons within a metre cube
Direction of conventional current
Positive to negative
Direction of electron current
Negative to positive
What is the charge on an electron?
-1.6x10^-19 C
How many electrons are needed to produce 1C?
6.5x10^18
Where does internal electrical resistance come from?
-In battery, chemical energy used to make electrons move
-Electrons colliding with atoms/ions in the battery
Does the current in series stay the same across the circuit or split?
Stays the same
Does the current in parallel stay the same across the circuit or split?
Splits
Does the potential difference in series stay the same across the circuit or split?
Splits
Does the potential difference in parallel stay the same across the circuit or split?
Stays same
What is Kirchhoff’s 1st law?
Total charge when reaching a junction is equal to total charge leaving a junction
What is Kirchhoff’s 2nd law?
Potential difference is the same over all components in a closed circuit
Equation for resistance in series
RT = R1 + R2
Equation for resistance in parallel
1/RT = 1/R1 + 1/R2
Why is an ammeter connected in series?
Very small resistance, meaning small voltage
Why is a voltmeter connected in parallel?
Large resistance, meaning small current
How can maximum power be reached?
When internal resistance and resistance are the same
How can emf and total resistance in series be calculated?
Take a sum
How can emf of several cells be calculated in parallel?
It is conserved throughout
How to determine output voltage in potential divider circuits?
Ratios of resistances
or equation
What are 4 different charge carriers?
-Metals (electrons)
-Electrolytes (positive/negative ions)
-Plasma (electrons and positive ions)
-Semiconductors (electrons and/or positive ‘holes’)
Define drift velocity
Average velocity that electrons gain in a material, due to an electric field
How does the cross-sectional area affect resistivity?
Greater area = easier the passage of electrons
How does length affect resistivity?
Longer = harder to send current through
How does resistance affect resistivity?
Larger resistance = higher resistivity
Define superconductor
Materials with no resistivity at and below a critical temperature
Uses for superconductors
- Reduce energy loss
- produces strong magnetic fields
What happens to resistance in a LDR when light intensity increases?
Resistance decreases
What happens to resistance in a negative temperature coefficient thermistor when temperature increases?
Resistance decreases
What happens to resistance in metallic conductors as temperature increases?
Resistance increases
