Physics - Controlled Assessment P1 Flashcards
For the hypothesis, what are the independent, dependent and control variables?
IDV: light intensity
DV: resistance
Control: same bulb/lamp,
same ambient light e.g. All curtains closed and lights off,
either distance between the LDR and lamp or the surface area of the LDR un/covered.
Same current flowing through to the LDR.
Same LDR.
What’s the context and how does the investigation relate to the context.
Light dependent resistors can be used for automatic light control and can be used to control when street lights turn on.
As light intensity increases, there is a change in current. This can be detected electronically and used to switch street lights on or off.
Why was this hypothesis made?
By carrying out this investigation, we shall see that increasing light energy will increase the supply of energy to the electrons in the LDR which will increase their ability to flow, being a photo-conductive cell.
This should cause the resistance to decrease.
The LDR is made up of a semi-conductor material where the outer electrons are weakly bounded to the atoms.
This means that, when bright light shines onto the LDR, resistance is much lower since light energy is transferred to the outer electrons of the atom and they break free.
This should enable them to be free to flow through the LDR and so this change in resistance could allow LDRs to be used for controlling switches.
Which sources did you choose and why?
I chose the New Physics for You - Investigating an LDR source because it has clear diagram showing a simple way to set up the equipment and a results table which could be used be used.
The second source was also useful as it provided a diagram showing equipment too however I found this source more useful as it has a graph showing what the outcome of our results should be like and additionally, in the method, uses a multimeter instead of an ammeter which would be easier for our investigation as we want to identify the resistance.
How would you do a preliminary investigation and how would you use this to decide an appropriate interval.
I would carry out my investigation, keeping the ambient light and type/wattage of the bulb the same so that it doesn’t affect the investigation then I I’ll measure the dependent variable - resistance using different intervals for the distance between the lamp and LDR.
I will use different intervals of 5cm, 10cm and 15cm from 0-50cm.
I’ll then choose the value that provides the best range of results.
Too large an interval and the results will have a big difference from each other which may not show a pattern.
To small an interval and there won’t be much difference between the results, especially if a low resolution is used.
Why check an investigation with others afterwards?
You can see if you got the same results or not.
Can find a more accurate average due to having more results, reducing the effect which errors have on the results.
It helps identify of the results are repeatable, reliable and reproducible.
What are the risks with this investigation?
Lamp bulb - hot and you can burn yourself if you touch it - don’t touch the bulb and move the lamp by its base.
Exposed wires - an electric shock - don’t touch exposed wires.
What’s the method?
Gather and set up the equipment
Connect the LDR to the multimeter, used to measure the dependent variable.
Switch on the lamp and position it 0cm away from the LDR, shining the light directly at the LDR. Record the reading of the resistance from the multimeter.
Move the lamp 10cm away, using a ruler for accuracy and allow the multimeter to adjust before taking another reading.
Repeat the step, moving the lamp at an interval of 10cm, ranging from 0-50cm
You should repeat the experiment 3 times to help identify anomalous results and calculate an average.
By moving the light source away from the LDR, the light intensity should decrease, resulting in the resistance increasing which would prove the hypothesis.
What equipment is needed?
Multimeter Ruler Wires and crocodile clips LDR Light source / desk lamp
What’s the hypothesis?
The resistance of an LDR (light dependent resistor) will decrease as the light intensity of a lamp bulb increases.
