LDR

Question 1

What are 3 uses of LDR

Answer 1

automatic street lights

sports games

brightness meters on smartphones

Question 2

What are LDR’s made out of, and how it looks like

Answer 2

cadmium sulfide which is made into flat disc on surface of LDR

Question 3

What changes the number density of charge carriers in LDR

Answer 3

intensity of the incident light

Question 4

Whats the resistance of LDR in dark conditions and why

Answer 4

very high resistance, because number density of charge carriers inside semiconductor is very low, so R is very high. Oftern into Mega ohms

High R

Question 5

Whats the resistance of LDR in brigher conditions and why

Answer 5

When light shines onto the LDR, number density of charge carriers increases dramatically, leading to rapid decrease in resistance of this component.

low R

Question 6

How to carry out an investigation for how resistance of LDR varies with distance from light source

Answer 6

1. use a light source like a filament lamp
2. use a narrow tube made of black cardboard placed around LDR to reduce background sources of light
3. vary the distance using meter ruler

Question 7

what would a resistance and light intensity graph look like. include labels for axis

Answer 7

ohms y axis

Wm^-2 x axis for light

curve decreasing gradient, high R means low Light

low R means high light

Question 8

How are LDR´s used for space

Answer 8

Some LDR´s are very sensitive to infrared radiation, so are useful as sensors for the very dim infrared recieved from space

Question 9

Why use infrared telescopes rather than eyes

Answer 9

eyes cant detect infrared wavelengths so using telescope we can discover more bout universe than we could before

Question 10

In astrophysics what can you see with infrared, and what does this allow us to see further.

Answer 10

dense clouds of dust with infrared, which passes through these clouds.

Which allows us to see new stars forming in stellar nurseries and to peer into very centre of our galaxy.

Question 11

Compare resistor, LDR, and thermistor

Answer 11

A resistor´s resistance is constant, so it follows ohms law, so we can call it an ohmic conductor.

The resistance of the resistor stays constant no matter any external factors unlike thermistor and LDR.

The resistance of LDR depends on the intensity of the incident light measued in Wm^-2 in si units.

The higher the intensity of the light, the lower the resistance, and vice versa.

For a thermistor, the resistance is dependent on the temperature.

As temperature increases, the resistance decreases, this is due to change in number density of charge carriers ie electrons and because negtaive temperature coefficient.

Thermistor and LDR have not got constant resistance so it does not follow ohm´s law.