Resistance & V= I X R Flashcards
What does the filament lamp graph show in terms of resistance?
As the temperature of the filament increases the resistance increases creating a curve
In a diode , where does current flow?
Current will only flow through a diode in one direction. The diode has very high resistance in the opposite direction
What is the equation involving potential difference, current and resistance?
P.D = current X resistance
V = I X R
What is a diode?
A diode is a special device made from semiconductor material such as silicon.
What is a diode used for?
It is used to regulate the potential difference in circuits
What does a light emitting diode do ?
A light emitting diode (LED)emits a light when a current flows through it in the forward direction
Why are LEDs commonly used in lighting?
They use a much smaller current than other forms of lighting
What is a light dependent resistor “LDR” ?
And LDR is a resistor that is dependent on the intensity of light
How does the LDR work?
In bright light the resistance falls.
In darkness the resistance is highest.
What is a thermistor?
A thermistor is a temperature dependent resistor
How does a thermistor work?
In hot conditions the resistance drops.
In cool conditions the resistance goes up.
What are thermistors useful to make?
Temperature detectors such as a car engine temperature sensor
What are the units of resistance?
Ohms
Write down the formula that links potential difference, work done and charge
P.d = work done \ charge
Give one use of a light dependent resistor LDR…
Automatic night lights
Outdoor lighting
Burglar detectors
What happens to the resistance of a thermistor as temperature increases?
It decreases
Explain why the resistance of a filament lamp increases as the temperature of the filament increases… (3)
As electrical charges flow through the filament some of the electrical energy is transferred into heat energy. This causes of the ions in the filament to vibrate more which makes it harder for the charges to move through the filament so the resistance increases.
Give one advantage of using LEDs instead of filament lamps
They use a smaller current
What are the three most important potential difference current graphs?
1) different resistors
2) filament lamp
3) diode
