• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month
Page
1. 1
1
2. 2
2
3. 3
3
4. 4
4

# Investigating how distance affects the light shining on the L.D.R.

Extracts from this document...

Introduction

RachaelSmith                                                                                                 Nov 2003

G.C.S.E Physics LDR Coursework

Planning

I am investigating how distance affects the light shining on the L.D.R.

An L.D.R is a light dependent resistor (LDR) is not so easy to see. It is a component that has a small transparent end which is sensitive to light. A change in the amount of light falling on it changes its resistance. This change in resistance can be used to switch a circuit on or off.

They are used in street lamps to switch them on in the evening and off in the morning. One other use is on bowling alleys. If your foot slides past the foul line, then you break a beam of light across this line. The LDR reacts to this, and a buzzer sounds. Similarly LDR’s can be used in burglar alarm circuits.

The Input is the distance of the bulb from the L.D.R. The out put is the mA.

These are some variables that could affect my results.

 Variables What effect will they have on the outcome? What voltage the bulbs at. If it’s at the same each time recorded at a certain length. Then the results will be recorded correctly, but if the power of the bulb isn’t the same it won’t be. Amount of daylight It would be an unfair test if there were different amounts of day-light at different readings. Shadows from people & objects. E.g. wires. Shadows will cover up light from the bulb, making the mA decrease. Distance between the bulb and L.D.R. Go down in 5’s to make it a fair test and keep it at that while recording so it doesn’t move (the mA).

Middle

Find out what the ammeter reads without the bulb light (this is the daylight).

Then record what the ammeter reads as you move the bulb 5cms nearer to the L.D.R each time, but take the reading of no bulb light away from them.

Observing

 Distance from L.D.R   (cm) 1st reading with daylight (mA) 2nd reading with daylight (mA) 55cm 7.3 7.3 50cm 7.5 7.5 45cm 7.6 7.4 40cm 8.4 8.0 35cm 9.5 7.8 30cm 10.5 8.3 25cm 10.3 10.8 20cm 11.9 13.2 15cm 17.1 15.2 10cm 26.2 24.5 5cm 55.7 51.8

We found out the reading for daylight which is 6.8mA and took this away

Conclusion

If the light beam is more intense, then more bonds are broken. So the LDR’s resistance decreases when you bring the light source closer. And the resistance increases as you move the light away. This is because it all depends on how much the light spreads out, when the LDR is near to the light there is a small distance so it misses less light. But when the LDR is further away from the light there is a bigger distance and so it misses more light. See diagram on next page.

Evaluating

I think maybe at 45cms we had shadows covering the light a bit so the recordings (mA) varied.

Overall the experiment was fairly accurate. A thing that may vary the recordings to make the points off the best fit line is the angle of the bulb as it could be a few millimetres off. To extend this investigation we could put tissue paper or something in front of the bulb to measure how much light is absorbed.

Page  of

This student written piece of work is one of many that can be found in our AS and A Level Electrical & Thermal Physics section.

## Found what you're looking for?

• Start learning 29% faster today
• 150,000+ documents available
• Just £6.99 a month

Not the one? Search for your essay title...
• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month

# Related AS and A Level Electrical & Thermal Physics essays

1. ## physics sensor coursework

The sensitivity of a sensor is the ratio of change of output to input. As the graph does not show linearity, the sensitivity of the sensor is different at various light intensities. The change in sensitivity is very rapid though.

2. ## The Relationship Between the Input and Output of an LDR

Circuit Diagram 2: Battery pack, fixed resistor and LDR connected in series. Voltmeter and the LDR connected in parallel. This is a potential divider circuit. Apparatus Diagram: Safety In this experiment, the dangers are only that the bulb could become very hot so there is a small risk of burns (particularly to the hand).

1. ## Choosing a light source

during normal operation as a result of the gas discharge Fluorescent tube lights are designed to operate within a specific temperature range. Temperatures below the range cause reduced output. Most are for indoor use, but there are models available for outdoor use.

2. ## The aim of my investigation is to investigate how the brightness (intensity) of light ...

The more the distance, the more external light will interfere. However we must have external light for safety reasons. Without external light, accidents could occur, which could result in bulbs or anything else dangerous breaking. This would be extremely dangerous as the broken glass of the bulb or anything else sharp can hurt someone.

1. ## Fire Alarm Investigation

I may get burnt by the Bunsen burner as it can get very hot and this can burn my skin. As this is electricity I don't know if the circuit may just blows, this is another factor. As you see there are lots of safety issues to contemplate during the investigation.

2. ## Build an effective sensing circuit that will be able to measure changes in light ...

(2) Resistance of LDR in k? (3) Resistance of LDR in k? (Average) 0 76.6 +/- 0.1 76.2 +/- 0.1 76.8 +/- 0.1 76.5 +/- 0.1 5 1.61 +/- 0.1 1.59 +/- 0.1 1.63 +/- 0.1 1.62 +/- 0.1 24 1.2 +/- 0.1 1.2 +/- 0.1 1.25 +/- 0.1 1.22 +/- 0.1 36 0.96 +/- 0.1 0.95

1. ## Using an LDR to detect the intensity of plane polarised light allowed through a ...

The fact that it has a slow reaction time could perhaps be an advantage, since it means that I will be able to use moving coil meters or digital multimeters without having to worry about it change before I can take a reading.

2. ## Sensors cwk. The aim of this coursework is to construct a potential divider circuit ...

One way to do this is to make the movement of the float turn the spindle of a rotary potentiometer. This is precisely what I did in my experiment. I made a hole with the same diameter as the spindle in one end of the cardboard.

• Over 160,000 pieces
of student written work
• Annotated by
experienced teachers
• Ideas and feedback to
improve your own work