12.4- COMPONENTS AND THEIR CHARACTERISTICS Flashcards
What is a cell a source of?
electrical energy
What is a battery a combination of?
combination of cells
What does a diode allow?
current in one direction only
What does a light-emitting diode (LED) do when it conducts?
emits light when it conducts
What is the direction that a diode conducts referred to as?
its forward direction
What is the opposite direction that a diode conducts referred to as?
reverse direction
Example of use of diode?
protection of dc circuits
What is a resistor designed to have?
certain resistance
What happens to the resistance of a thermistor as the temp increases, if the thermistor is an intrinsic semiconductor i.e. silicon?
resistance decreases
What happens to the resistance of a light-dependent resistor (LDR) with increasing light intensity?
resistance of LDR decreases with increasing light intensity
To measure the variation of current with pd for a component, what should you use? (2)
potential divder to vary pd from zero
OR
variable resistor to vary current to minimum
What is the advantage of using a potential divided when measuring the variation of current?
current through component + pd across it can be reduced to zero
not possible with variable resistor circuit
What kind of IV graph does a wire give?
straight line through origin
What does the IV graph of a wire being a straight line through the origin mean?
means that any point on line, value of V/I same
resistance constant
What kind of IV graph does a filament bulb give and why?
curve with decreasing gradient as its resistance increases as it becomes hotter
What kind of IV graph does a thermistor at constant temp give?
straight line
higher the temp, greater the gradient of the line- resistance falls with increase of temp
What else has has the same IV graph as a thermistor at constant temp?
LDR in respect of light intensity
Above what pd does a silicon diode conduct easily in its forward direction?
above pd of about 0.6V and hardly at all below 0.6V or in opposite direction
How does the resistance of a metal change with temperature?
resistance of metal increases with increase of temp
Why does the resistance of a metal increase with increase of temp?
as positive ions in conductor vibrate more when its temp increased
so conduction electrons cannot pass through metal as easily when pd applied across conductor
Why is a metal said to have a positive temperature coefficient?
as its resistance increases with increase of temperature
How does the resistance of an intrinsic semiconductor change with temperature?
resistance of intrinsic semiconductor decreases with increase of temp
Why does the resistance of an intrinsic semiconductor decreases with increase of temp?
number of conduction electrons increases when temp increased
What is a thermistor made from?
an intrinsic semiconductor
