4.2 - Electricity - Energy, Power and Resistance Flashcards
What is potential difference (V)
It is used to measure the work done by charge carriers, which lose energy as they pass through the components in a circuit,
What is potential difference (V) defined as
The energy transferred from electrical energy to other forms per unit charge
What equation contains potential difference, energy and charge
V = W/Q
What is 1 volt defined as
1 joule of energy transferred per coulomb
What is electromotive force (e.m.f)
Is it the work done to charge carries, when they gain energy as they pass through a cell or power supply
What is the difference between voltage and emf
Voltage is energy transferred per coulomb across a load resistance.
Emf is the total amount of work done by the battery per coulomb
Is the kinetic energy of an electron is multiplied by its charge multiplied by the voltage
Yes, Energy transferred = eV = 1/2 x m x v^2
What is the equation for resistance
R = V/I
What is resistance defined as
The potential difference across the component, divided by the current in the component.
What is resistance
How difficult it is for current to flow through an appliance.
What is the definition of 1 Ohm
When a resistor is subject to a voltage of 1V and allows a current of 1A through
What is an ohmic conductor
A conductor that obeys Ohm’s law
What is Ohm’s law
The current through an ohmic conductor is directly proportional to the potential difference across it. (resistance doesn’t vary with voltage or current)
(only true if constant temperature)
What graph represents an ohmic conductor
A line that has a constant gradient (straight line) and passes through the origin
On a I V graph what shows a higher resistance
A smaller gradient means a higher resistance
What graph represents a non ohmic conductor
Scoops at the bottom left going up through the origin then begins to curve over.
What is an example of a non ohmic conductor
Filament lamp where as current increases so does resistance
What graph represents a diode
Flat when the voltage is negative or 0 then has a curved increase (not present in negative current as in diode current only flows in one direction)
What is a light dependent resistor (LDR)
A semiconductor that is sensitive to light, as light intensity increases the resistance decreases (brighter = more resistance)
What is a thermistor
As the temperature increases the resistance decreases (thermistors that work this way are called negative temperature coeficcient)
What is resistivity
The resistivity of a metal shows how east or difficulty it is for current to flow in the material (at a specific temperature)
What is the resistivity equation
p = RxA / L
( resistivity = resistance x cross sectional area / length )
What is the experiment to determine resistivity of a metal
Take a wire use a micrometeor to measure diameter then calculate area. Vary length in wire and record voltage and current. Use R=V/I to work out resistance. Plot a graph of resistance against length. Gradient = resistivity / area. resistivity = gradient x area
What is power
Rate of energy transfer
What is the equation for power
P = V x I
Why are kilo watt hours (kWh) used
As joules and watts are both too small so to be more practical and make the numbers smaller for people electrical companies use kWh
Equation to find cost of electricity
Total cost = units x price
