Electricity Flashcards
Current
The rate of flow of charge around a circuit
What is current caused by?
The movement of charged particles
An ideal ammeter has?
Zero resistance as it would change the current
Electrons flow from
The negative terminal to the positive terminal
Potential Difference
Work done per unit charge
An ideal voltmeter has ?
Infinite resistance
Resistance
A measure of opposition to the flow electrons through the component
Ohm’s Law
The pd across an ohmic conductor is directly proportional to the current flowing through it provided physical contact do not change
The gradient in an IV graph
Resistance = 1/gradient
IV characteristics of a resistor
Low resistance = Steep gradient
High resistance = Shallow gradient
Resistivity
Measure of how much opposition to the flow of electrons a conductor has
Constant value
Equation for resistivity
Resistivity = RA/L
The resistance of a wire is….
Inversely proportional to the area and inversely proportional to the length
Junction Rule
At any junction in the circuit, the total current entering the junction is equal to the total current leaving the junction
Loop rule
For any closed loop in a circuit, the sum of the emfs around the loop is equal to the sum of the potential drops
Power
The rate of energy transfer (Watts)
Power equation 1
Power = Current x Potential Difference
Power equation used in series
P = I^2 x R
Power Equation used in parallel
P = V^2/R
Variable Resistor
Used to vary the current to a minimum when placed in series to a component
Potential Divider
An arrangement of resistors
Advantage and disadvantage of variable resistor
Adv - Easy to connect
Dis - Current through a component can never be = 0 - variable resistor is set to it’s max resistance
Advantages and disadvantages of potential dividers
Adv - current through the component and Pd can be reduced to 0
Disadv - wastes power
Charge is ?
The fundamental property of matter
How to calculate the number of electrons in one Coulomb?
1/(charge of an electron)
Charge of an electron = 1.6 x 10^-19
What can a variable potential divider be used for?
Change the output voltage with a fixed pd of supply
Why does the resistance decrease with an increase in temperature in thermistors?
The number of charge carriers increases with an increase in temp as electrons break from from the atoms of the semiconductor
Therefore, there is a greater current and the resitance decrease
Resistance- temp graph of thermistor
Decrease in resistance as temp increases is non linear
Almost like the letter L
I/V characteristic of a thermistor
Thermistor with higher temp is steeper
Thermistor with lower temp is shallower
Constant temp = straight line
Higher temp (non constant) gradient increase
Resistance of an LDR?
Decreases as light intensity increases
Same as thermistor but with light
Superconductor
Material with 0 resistivity at and below the critical temperature
Superconductivity
Property of superconductors
Critical temperature
Temperature at and below which a superconductor has 0 resistivity
Superconductors graph
Resistance-Temp graph
Straight line going along x axis
Shoots up at critical temperature
Then slow starts increasing gradient then quickly rises u
When the temperature drops to the critical temperature?
The resistivity of the superconductor will suddenly drop to 0
Superconductors can be used to make?
High power electromagnets and generate very strong magnetic fields
Used in particle accelerators and MRI scanners
Expel magnetic fields and repel magnets
Electromotive force
Electrical energy per unit of charge produced by the source
EMF > Terminal PD
Terminal pd
Electrical energy per unit charge that is delivered to external components
Internal resistance
Resistance of materials within the battery
OR
The loss of potential difference per unit current in the source
Equation for EMF
EMF = I(R + r)
EMF (V) - EMF Force
I (A) - Current
R (Ohms) - Resistance of components in the circuit
r (Ohms) - Internal resistance
Other equation for EMF
EMF = V + Ir
Where V = terminal PD
