3.5.1 Electricity Flashcards
Define electric current
The rate of flow of charge
Define potential difference
The work done per unit charge
Define resistance
The ratio of voltage to current
Describe ohms law
The potential difference across a component is directly proportional to the current through it when under constant physical conditions.
(V = IR)
What is the ideal resistance of an ammeter and voltmeter?
Zero and infinite respectively
What is resistivity?
The extent to which a material opposes electrical current through it at a given temperature
What happens to the resistance of a metal conductor and ntc thermistor when temperature is increased?
Metal conductor- resistance increases
Ntc thermistor- resistance decreases
How can superconductors be used?
Strong magnetic fields:
MRI scanners, mag lev trains, particle accelerators
Reduced energy loss:
Superconductor cables
Describe a superconductor
A material that has a resistance and resistivity of 0 when below a critical temperature
How is total resistance calculated in a series circuit?
Rt = R1 + R2 + R3 + …
How is total resistance calculated in a parallel circuit?
1/Rt = 1/R1 + 1/R2 + 1/R3 + …
What must be conserved in dc circuits?
Charge and energy
Draw the IV graph for a semiconductor diode
What is Kirchhoff current law?
The total current flowing into a junction = the total current flowing out of a junction
What is Kirchhoff voltage law?
The sum of the voltages from the cells = the sum of the voltages across each component
What is a potential divider circuit?
Two or more resistors connected in series with a source of potential difference
What resistors can be used in a potential divider circuit?
Variable resistors, thermistors, LDRs and fixed resistors OR a potentiometer
How can a potential divider circuit be used for a night light?
Use an LDR with a filament bulb connected in parallel to it and a fixed resistor.
When light intensity decreases the LDR resistance will increase causing it to recieve a greater proportion of the voltage.
Define emf
The work done moving 1 column of charge through the cell
OR
the amount of energy converted to electrical energy for each 1 column of charge moving through the cell
What causes internal resistance?
Electrons collide with atoms loosing energy to heating
What is the terminal PD?
The emf - the lost volts
How do you Calculate the total emf and internal resistance of cells in series?
EMF = emf1 + emf2
Internal resistance = internal resistance1 + internal resistance 2
How do you calculate the total EMF and internal resistance of cells in parallel?
EMF = E1 or E2
Internal resistance = internal resistance1 / number of cells in parallel
