12.4 Components and their characteristics Flashcards
What is a cell
A source of electrical energy
What is a battery
A combination of cells
What is the symbol for an indicator the same as
For a light source including filament lamp but NOT an LED
What is a diode
Allows current in one direction ONLY
LED emits light when it conducts
What is the direction in which a diode conducts referred to
As its forward direction
What is the direction opposite to which a diode conducts referred to
As its reverse direction
What are diodes used for
The protection of dc circuits for example, in case the voltage supply is connected the wrong way around
What is a resistor
A component designed to have a certain resistance
How does the resistance of a thermistor change as temperature increases
The resistance decreases if it is an intrinsic semiconductor such as silicon
How does the resistance of a light-dependent resistor (LDR) change as light intensity increases
The resistance decreases
What does LDR stand for
Light-dependent resistor
What does LED stand for
Light-emitting diode
How to measure the variation of current with pd for a component
Use either a potential divider to vary the pd from zero or a variable resistor to vary the current to a minimum
What is the advantage of using a potential divider than a variable resistor
The current through the component and the pd across it can be reduced to zero which isn’t possible when using a variable resistor
What is the shape of the IV graph of a wire
A straight line through the origin
What is the shape of the IV graph of a filament bulb
Curve with a decreasing gradient because its resistance increases as it becomes hotter
What is the shape of the IV graph of a thermistor
A thermistor at constant temperature gives a straight line. The higher the temperature, the greater the gradient of the line, as the resistance falls with increase of temperature.
How does the resistance of a metal change when temperature increases
The resistance increases
Why does the resistance of a metal increase as temperature increases
This is because the positive ions in the conductor vibrate more when its temperature is increased. The charge carriers therefore cannot pass through the metal as easily when a pd is applied across the conductor.
Why is a metal said to have a positive temperature coefficient
Because its resistance increases with increase of temperature
How does the resistance of an intrinsic semiconductor change with an increase in temperature
The resistance decreases as the number of harge carriers (conduction electrons) increases when the temperature is increased. Therefore, a thermistor made from an intrinsic semiconductor has a negative temperature coefficient
