Question

In physics I am doing an experiment and the hypothesis is ''The light intensity falling on a LDR affects the resistance of the component.
There is one step in the method that I dont understand; 5) Then, move the lamp back at 20cm intervals until you reach a distance of 80 cm each time and record the resistance. Could someone please explain?

Answer 1

@aayushi.somani

Answer 2

@IrishBoy123

Answer 3

moving the lamp back will decrease the light intensity, probably following some inverse square law and thus cause an increase in the resistance of the ldr.

so "move the lamp back at 20cm intervals", i guess means starting with lamp at 20cm away from the ldr, then, then 40cm away , then 60cm, finally 80cm. record the resistance each time.

Answer 4

@IrishBoy123 what do you think will be the control variables in the experiment ?

Answer 5

hi @Sophhh786

what do you think?

brightness of torch
distance from ldr
ambient light
voltage load on resistor
type of ldr
age of ldr
ambient temperature

just thinking out loud.

Answer 6

@IrishBoy123 I think distance please tell me if I am correct

Answer 7

@matt101

Answer 8

@Sophh786

distance is the thing you are **changing** as that is how you are varying light intensity. the control variables OTOH are usually all the things that you need to keep **constant**. if you do not, then you cannot ascribe your results solely to the change in light intensity brought about by change in distance.


to take a silly example, if you use lamps of different intensity or light colour at the various points, your results could be quite meaningless.

i gave you a random list of things that you would need to keep the same. ie

brightness of torch
**distance from ldr** this is what you are changing, NOT a control variable
ambient light
voltage load on resistor
type of ldr
age of ldr
ambient temperature

all but one is a poss control variable. i am sure there may be others, eg angle of torch. colour of flight. pretty mucu everything might be a control variable so you should i guess just be practical about it.

Answer 9

so distance is the independent variable therefore I am going to have to vary how many cm it is away from the ldr right? @IrishBoy123

Answer 10

indeed, you are varying intensity by moving the torch, as the instructions you provided seem to indicate.

Answer 11

hey @IrishBoy123 My control variables are the angle of the light source (lamp) and the brightness how would this make my experiment a fair test ? Please help

Answer 12

For an experiment to be a fair test, you need to make sure that you change only one variable at a time.