12.4 Components and their characteristics Flashcards

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1
Q

What is a cell

A

A source of electrical energy

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2
Q

What is a battery

A

A combination of cells

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3
Q

What is the symbol for an indicator the same as

A

For a light source including filament lamp but NOT an LED

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4
Q

What is a diode

A

Allows current in one direction ONLY

LED emits light when it conducts

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5
Q

What is the direction in which a diode conducts referred to

A

As its forward direction

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6
Q

What is the direction opposite to which a diode conducts referred to

A

As its reverse direction

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7
Q

What are diodes used for

A

The protection of dc circuits for example, in case the voltage supply is connected the wrong way around

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8
Q

What is a resistor

A

A component designed to have a certain resistance

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9
Q

How does the resistance of a thermistor change as temperature increases

A

The resistance decreases if it is an intrinsic semiconductor such as silicon

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10
Q

How does the resistance of a light-dependent resistor (LDR) change as light intensity increases

A

The resistance decreases

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11
Q

What does LDR stand for

A

Light-dependent resistor

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12
Q

What does LED stand for

A

Light-emitting diode

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13
Q

How to measure the variation of current with pd for a component

A

Use either a potential divider to vary the pd from zero or a variable resistor to vary the current to a minimum

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14
Q

What is the advantage of using a potential divider than a variable resistor

A

The current through the component and the pd across it can be reduced to zero which isn’t possible when using a variable resistor

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15
Q

What is the shape of the IV graph of a wire

A

A straight line through the origin

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16
Q

What is the shape of the IV graph of a filament bulb

A

Curve with a decreasing gradient because its resistance increases as it becomes hotter

17
Q

What is the shape of the IV graph of a thermistor

A

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.

18
Q

How does the resistance of a metal change when temperature increases

A

The resistance increases

19
Q

Why does the resistance of a metal increase as temperature increases

A

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.

20
Q

Why is a metal said to have a positive temperature coefficient

A

Because its resistance increases with increase of temperature

21
Q

How does the resistance of an intrinsic semiconductor change with an increase in temperature

A

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