S6 electricity - 2. I/V Characteristics

Question 1

draw an I/V graph for an ohmic conductor at a constant temperature

Answer 1

• A straight line through the origin
• should look like a y=x graph

Question 2

draw an I/V graph for a filament lamp

Answer 2

• Should look like an S curve (it goes through the origin)

Question 3

what happens to the resistivity of metal as temperature increases?

Answer 3

The resistance of a metal increases as the temperature increases

Question 4

draw an I/V graph for a diode

Answer 4

• should look like an exponential graph. with a flat line until 0

Question 5

describe why an ohmic conductor has a straight line

Answer 5

Since the current through an ohmic conductor is directly proportional to the voltage (at constant temperature) the resistance is constant. Therefore, the line would have the same gradient making it straight.

Question 5

describe why an ohmic conductor has a straight line (I/V characteristic)

Answer 5

Since the current through an ohmic conductor is directly proportional to the voltage (at constant temperature) the resistance is constant. Therefore, the line would have the same gradient making it straight.

Question 6

describe why a filament lamp has a curved line (I/V characteristic)

Answer 6

the curve in a filament lamp starts steep but gets shallower as voltage increases.

Since it has a coiled-up length of wire it can get hot as the current flowing through the lamp increases its temperature.

Since the resistance of metal increases as the temperature increases the curve gets shallower causing less current to go through.

Question 7

how do you work out the resistance of … from a graph

Answer 7

Find the value of V and I, then use the formula R= V / I

DONT USE GRADIENTS ITS A COMMON MISTAKE

Question 8

Why are semiconductors considered inefficient to conduct electricity?

Answer 8

There are far fewer charge carriers available

Question 9

why are semiconductors great sensors?

Answer 9

They don’t conduct electricity as much as metals since there are far fewer charge carriers.

however, if energy is supplied to the semiconductor, more charge carriers can be released, this makes them great sensors for detecting changes in their environment

Question 10

what is a thermistor?

Answer 10

A thermistor is a resistor with a resistance that depends on its temperature

Question 11

what does NTC stand for?

Answer 11

Negative temperature coefficient

Question 12

what does NTC thermistor mean?

Answer 12

This means the resistance decreases as the temperature goes up

Question 13

why are higher temperatures lowering resistance in thermistors?

Answer 13

Heating up thermistors gives more electrons enough energy to escape from their atoms. This means there are more charge carriers available, so the resistance is lower

Question 14

state the key property of a diode

Answer 14

Diodes (including light emitting diodes [LED’s]) only let current flow in one direction

Question 15

what is forward bias?

Answer 15

forward bias is the direction in which the current is allowed to flow

Question 16

what is the threshold for most diodes?

Answer 16

Most diodes require a threshold voltage of around 0.6V in the forward direction before they conduct

Question 17

What happens at reverse bias?

Answer 17

At reverse bias, the resistance of the diode is very high and the current that flows is very tiny.