Section 6 - Electricity Flashcards
(27 cards)
Define the term current.
Current is the rate of flow of charge in a circuit
How are ammeters attached to a circuit.
In series
Define the term potential difference
The potential difference between two points is the work done in moving charge between the points
What is meant by Resistance
The resistance of something is a measure of how difficult it is to get a current to flow through it, it is defined as R = V ÷ I
What is Ohms law
Provided the physical conditions, such as temperature, remain constant, the current through an ohmic conductor is directly proportional to the potential difference across it.
What happens to the resistance of an ohmic conductor if you double the potential differnece across it?
Nothing - the resistance of an ohmic conductor is constant
What resistance do you normally assume a voltmeter / ammeter to have
Voltmeter -infinite resistance
Ammeter - 0 resistance
Is a filament lamp an ohmic conductor
A filimant lamp is not an ohmic conductor. It’s characteristic IV graph is not a straight line, so therefore voltage is not proportional to current
State the three things that the resistance of a material depends on.
Length Area Resistivity
What is resistivity
The resistivity of a material is the resistance of a 1m length with a 1 m^2 cross sectional area. it is measured in ohm-meters
Describe the effect of temperature on the resistance of a metal
As the temperature of a metal increases, its resistance will also increase
What is a superconductor
A material that has zero resistivity when cooled below a critical temperature (called the transitional temperature)
What are some disadvantages of superconducting wires
- It is very difficult to cool a material below its transitional temperature
- It is very expensive to keep a material below its transitional temperature
Give some uses of superconducting wires
- Power Cables
- Strong Electromagnets
- Fast electronic circuits
State the equation used to calculate the cross-sectional area of a cylindrical wire
Area = pie*r^2 assuming its circular
Define the term power
Power (P) is the rste of transfer of energy. It’s measured in Watts (W), where 1 watt is equivalent to 1 joule per second.
Write down three equations you could use to calculate electrical power
P=VI
P=V^2/R
P=(I^2)R
Explain why batteries have an internal resistance
In a battery, chemical energy is used to make electrons move. As they move, they collide with atoms inside the battery and lose energy - this is the internal resistance
What is the load resistance of a circuit
The load resistance is the total resistance of all the components in the external part of the circuit
What units is electromotive force measured in
Volts
Explaim what lost volts are
The energy wasted per coulomb overcoming an internal resistance
What do the gradient and vertical intercept on a V-I graph for a power supply show
The gradient is -r (where r is internal resistance)
The verticle intercept is E (the electromotive force)
State Kirchoff’s first law
The total current entering a junction = the total current leaving it
State Kirchoff’s second law
The total e.m.f around a series circuit = sum of the p.d.s across each component
