Electrical Components and Energy

Created by

Sophie

Cards (27)

What is a variable resistor?
Used to control the current flowing in a circuit and it changes the potential difference across a component.
Define current:
The rate of flow of charge
What is potential difference?
The amount of energy transferred per coulomb of charge
This is Ohm's Law graph where there is a straight line through the origin. A wire and resistor obey Ohm's Law. They are Ohmic.
What is Ohm's Law?
The current is directly proportional to the potential difference for a constant temperature.
How does voltage affect the current through a filament lamp?
The current is not directly proportional to the potential difference so a filament lamp does not obey Ohm's Law (non-ohmic).
As the potential difference increases the temperature of the lamp increases. Therefore, the atoms vibrate more creating a greater resistance for the current to flow through.
How does voltage affect the current through a diode?
A diode does not obey Ohm's Law (non-ohmic).
A diode only allows current to flow in one direction.
As voltage increases so does the current.
Resistor I-V graph
Current is directly proportional to potential difference (voltage)
A resistor is Ohmic.
Wire I-V graph
Current is directly proportional to potential difference (voltage).
A wire is Ohmic.
Filament lamp I-V graph
Current is not directly proportional to potential difference.
A filament lamp is Non-ohmic.
Temperature and resistance increase as potential difference increases.
Diode I-V graph
Current is not directly proportional to potential difference.
A diode is Non-Ohmic.
Diodes only allow current to flow in one direction.
What is a thermistor?
A resistor that changes resistance with the temperature.
How does resistance change when the temperature changes?
The resistance of a thermistor decreases as the temperature increases.
The rate of change of resistance decreases as the temperature increases, or the gradient decreases.
What is a Light Dependent Resistor (LDR)?
A resistor that changes resistance with a change in light intensity.
How does resistance change when light intensity changes?
The resistance of an LDR decreases as the light intensity increases.
The rate of change of resistance decreases as the light intensity increases, or the gradient decreases.
Sensing temperature- switching on a fan
When the temperature increases the thermistor resistance decreases.
Therefore, it takes a smaller share of the potential difference.
The fixed resistor takes a larger chare of the potential difference and the fan turns on/goes faster.
e.g. in air conditioning or a cooling system
Sensing light level- switching on a lamp
The LDR takes a bigger share of the potential difference when it gets dark.
Therefore the lamp turns on/gets brighter.
e.g. in a street lamp
Define power
The amount of electrical energy that is transferred every second.
Measure in Watts
Energy transferred by appliances examples:
Kettles transfer energy electrically from the mains ac supply to the thermal store of the heating element.
Energy is transferred electrically from the chemical store of a battery to the kinetic energy of the fan blades.
The amount of energy the appliance transfers when it is on depends on:
Potential difference of the supply
Resistance of the appliance
Current flowing in the circuit
Time it is on for
What are the 2 equations linking power, current and potential difference?
power = current X potential difference
P = I X V
P = I $^2$ X R
What circuit symbol is this?
Resistor
What circuit symbol is this?
fuse
what circuit symbol is this?
Variable resistor
What circuit symbol is this?
Light dependent resistor
what circuit symbol is this?
Diode
what is the equation linking energy transferred, power and time
energy transferred = power x time