Electricity U1.9-1.2 Flashcards
What is the definition of charge
One coulomb of charge passes a point in a circuit each second if a current of one amp flows
What is the definition of current
Rate of flow of charge
What direction is the flow of current
Current flows from positive to negative
What direction do electrons flow
From negative to positive
How does current act in parallel to series
Current is the same everywhere in a series circuit
Current splits across branches in a parallel circuit
What is the definition of Potential Difference / Voltage
The p.d between two points in a circuit is the electrical energy changed into other forms for each coulomb of charge which flows between the points.
What happens if the p.d. Between two points in a circuit is equal to 0V
Then no current flows between those two points
How does voltage act in parallel circuits compared to series
Current splits in series circuits where as it is the same across each branch in a parallel circuit
What is the definition of resistance
Resistance is the ratio of voltage to current
What is resistance the opposition of
Current flow
When is resistance caused
When the free electrons collide with the atoms of a conductor
How do you calculate the total resistance of resistors in a series circuit
R1 + R2 + R3….
How do you calculate the total resistance of resistors in a parallel circuit
1/Rt = 1/R1 + 1/R2 + 1/R3…..
What is the definition of power
Rate of change of energy
What are the three equations for power
P=VI
P= I^2 R
P=V^2/R
What is ohms law
A conductor held at a constant temperature obeys ohms law is the p.d. Across it is directly proportional to the current flowing through it.
If it obeys it it is said to have ohmic behaviour
What is a super conductor
A super conductor is a material with an electrical resistance which drops to zero below a certain temperature, which is known as the transition temperature.
What is a transition temperature
This is the temperature below which the material becomes superconducting
Why are superconductors useful
They can carry large amounts of electrical current for long periods of time without loosing energy as heat.
What is the definition of resistivity
Resistivity is numerically equal to the resistance of a material of unit length and unit cross sectional area
What is the equation for resistivity
p=RA/l
Resistivity = Resistance x Area / Length
What is resistivity measured in
Ohm meters
What is the difference between resistance and resistivity
Resistance is a property of a particular conductor
Resistivity is a property which has a characteristic value for a given material
What is the definition of emf
The emf of a source is the amount of energy converted into electrical energy for each coulomb of charge passing through a source
What is the equation for emf
EMF = energy converted / charge
What is internal resistance
Sources such as batteries will have some opposition to the current which passes through them.
What are the equations for internal resistance
E=V+Ir
E=IR+Ir
E=I(R+r)
E = the emf of the supply in Volts.
I = the current in Amps.
R = the resistance in the external circuit.
r = the internal resistance of the supply
V = the p.d. Across the external circuit in Volts
What is the alternative definition of emf
The emf of a supply is equal to the p.d. Across its terminals when it is not supplying current
What is the potential divider equation
Vout = Vin x R1/R1+R2
