Electric Circuits Flashcards
Define power
It is the rate at which work is done or the rate at which energy is transferred
The unit is the watt(W)
P = W/t
If a force causes an object to move at a constant velocity: P = Fv
Define one watt
It is the power when one joule of work is done in one second (1 J x s^-1)
Define power efficiency
It is the ratio of output power to input power
% efficiency = (power out / power in) x 100
Define potential difference
It is the work done per unit positive charge.
V=W/Q
Define current
It is the rate of flow of charge
I=q/t
State ohm’s law
Ohm’s law states that current through a conductor is directly proportional to the potential difference across the conductor at constant temperature
Ohmic conductors
Ohmic conductors obey Ohm’s law and have a constant resistance when voltage is varied across or current is increased
A graph of current vs voltage across these conductors will be a straight line
Example of ohmic conductors include circuit resistors and nichrome wire
Non-ohmic conductors
Non-ohmic conductors do not obey Ohm’s law. Their resistance changes as their temperature increases.
A graph of voltage against current will not be a straight line for these conductors to show that resistance is not constant over values of voltage and current
Examples include light bulbs, diodes and transistors
Define resistance
Resistance is the material’s opposition to the flow of electric current. The unit of resistance is the ohm
Properties of series circuits
Voltage equals to the sum of the individual voltage drops( V= V1 + V2)
Current is the same throughout the circuit
(A= A1 = A2 = A3)
Resistance equals to the sum of the individual resistances( RT = R1 + R2)
Properties of parallel circuits
Voltage is the same throughout the circuit (V=V1=V2)
Current equals to the sum of the current branches(A=A1+A2)
Resistance diminishes to equal a lower resistance (1/RT= 1/R1 + 1/R2)
Power and energy
Solve problems using electrical energy
W = Pt
Electrical energy is measured in joules( J )
Electrical power
The electrical power dissipated in a device is equal to the product of the potential difference across the device and current flowing through it
What is 1kWh
The kilowatt hour is a unit of energy.
1kWh is the amount of energy used when 1 kilowatt of electricity is used for 1 hour
Cost of electricity
Cost of electricity = Electrical energy (Power x time) x cost per unit
Formulae
P=VI
P=I^2R
P=V^2/R
P=W/t
W=VIt
W=I^2Rt
W=V^2/R x t
W=VQ
Define emf
It is the total energy supplied per coulomb of charge by the cell
