• 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
  5. 5
    5
  6. 6
    6
  7. 7
    7
  8. 8
    8
  9. 9
    9
  10. 10
    10
  11. 11
    11
  12. 12
    12

Light intensity

Extracts from this document...

Introduction

Year 11 assessed practical: light intensity

Hypothesis

  • A light bulb gives out light when electricity passes through it
  • The more volts you add, the more intense the light is. As you double the voltage, the light intensity doubles.
  • This is because the rays are more concentrated. The rays are twice as concentrated as the intensity doubles, as more power is running through the circuit
  • The LDR (Light dependent resistor) measures how intense the light is
  • The LDR frees up electrons, decreasing resistance
  • The more intense the light is, the lower the resistance in the LDR
  • Ohms law says that current increase is proportional to potential difference
  • This only occurs if all conditions are the same
  • As Potential difference doubles, Current doubles.
  • Resistance is voltage over current.
  • If voltage rises proportionally with current, then resistance will halve as voltage doubles.
  • So as I halve the voltage, the current halves, light intensity halves, and resistance doubles.

Method

This is how I will set up the apparatus. Below is a circuit diagram.

The set up of the circuit is simple as shown above. The 12-volt lamp is set up in a simple circuit. Then in a SEPARATE circuit, the light dependent resistor is connected to the Multimeter, which shows the resistance readings. If I did connect the LDR in the same circuit, I would almost certainly fry the LDR, and ruin the experiment! I want to keep the distance from the lamp to the LDR the same.

...read more.

Middle

Fair Test
  • Change only one variable (Voltage)
  • Keep distance from LDR to bulb the same
  • Make sure all readings are taken in darkest possible surroundings
  • Try to use the same bulb each time
  • Measure each voltage as accurately as the setting allows
  • Keep my experiment as far away from others as possible, to get minimal interfering light
  • Keep the height of the bulb above the LDR the same

Results table showing resistance of the LDR as potential difference (volts) are changed

Potential difference

(volts)

Resistance  of LDR 1 (Ohms)

Resistance  of LDR 2 (Ohms)

Resistance  of LDR 3 (Ohms)

Average Resistance of LDR (Ohms)

0.0

60,400

102000

107000

89800

2.0

50,200

35000

32000

39067

4.0

1005

1102

1168

1092

6.0

394

398

412

401

8.0

203

205

208

205

10.0

138.8

139.3

150.4

143

12.0

101.3

102.1

106.2

103

14.0

79

81.5

84.1

82

Distance of the LDR from the bulb kept constant (directly underneath the bulb, 0cm)

Analysis

On the previous page is the graph; now I will try to sum up the results.

As the potential difference increased, the resistance decreased, dramatically at first, indicated by the steep slope on the graph. As the Potential difference was increased further, the resistance continued to decrease, but more slowly.

At first (0.0 to 2.0, then 2.0 to 4.0) the resistance decreased three times, then thirty times as potential difference doubled. Later, as potential difference increased from 12 volts to 14 volts, then resistance didn’t even halve, but decreased by about 20%.

These are massive differences, and the reason for the large resistance readings at 0.0 and 2.0 volts is that the LDR sensed no light with which it frees electrons, therefore decreasing resistance. The bulb visibly gave out light at 4.

...read more.

Conclusion

These could all be incorporated into the method, and if I did this experiment again, I could add these extra points to the method

  • Keep a cover on the bulb to make sure all the light hits the LDR
  • Use the same practical equipment
  • Try to work as far away from other people as possible.

Other than that I think the method works well. I left out the points regarding letting the system cool down, as there is not enough time to do the experiment in, and I could certainly not use a whole day to take results. If I had the time, I would also try to take more sets of readings, up to 10 sets, to get the best graphs. However, the above points are a realistic way of improving my results next time.

...read more.

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

See related essaysSee related essays

Related AS and A Level Electrical & Thermal Physics essays

  1. To Investigate How the Resistance of the Light Dependent Resistor Depends On the Current ...

    The Variable factor Vary the current in the light bulb circuit by changing the resistance of the variable resistor. Safety: * As this experiment involves electricity, I will handle it carefully. * I am going to only use a voltage of three volts so the wire will not burn.

  2. Investigation into the resistance of a filament lamp.

    1.28 1.27 1.27 Bright red 7.00 1.32 1.31 1.33 1.32 Light orange 7.50 1.42 1.41 1.39 1.41 Normal orange 8.00 1.48 1.46 1.45 1.46 Normal orange 8.50 1.53 1.51 1.51 1.52 Bright orange 9.00 1.56 1.58 1.55 1.56 Bright orange 9.50 1.59 1.61 1.59 1.60 Normal yellow 10.0 1.64 1.62

  1. Characteristics of Ohmic and non-Ohmic Conductors.

    (Instead of doubling to 18.4 mA) Voltage range (volts) Current Range (mA) Gradient 0.1-0.2 6.6-9.2 0.026 0.3-0.4 10.7-12.1 0.014 0.5-0.6 13.5-14.7 0.012 0.7-0.8 16.0-17.0 0.010 0.9-1.0 18.1-19.0 0.009 This graph shows a complete curve. At the beginning of the graph the current is increasing at a high rate (the voltage is also increase but not at the same rate as the current).

  2. Characteristics of Ohmic and Non Ohmic Conductors.

    Non ohmic conductors are those that do not obey Ohms Law. This means that the resistance of these conductors changes with current and that the current and the voltage are not proportional. There are different non ohmic conductors. The non ohmic conductors are more useful in industry such as radio receivers.

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

    can't tap the voltage off at any point therefore we use two resistors instead. The voltage is then measured between the two resistors. The diagram below illustrates this: V1 is the voltage in and V2 is the voltage out. If we know V1, R1 and R2 we can use the

  2. Investigating The Characteristics Of A Light Bulb.

    0.19 2.05 0.20 2.15 0.20 2.25 0.21 2.35 0.21 2.45 0.21 2.55 0.22 I found that there was a trend from the current when I went up by 0.10, but the results were too close together so I decided to try going up by 0.20 volts.

  1. I aim to find out how distance affects the light intensity emitted from an ...

    To get the greatest voltage difference the fixed resistor (R2) should be the same resistance as the average of the LDR so half way between it highest and lowest reading. If it's set up exactly right it should read half the supply voltage.

  2. Light intensity notes

    Velocity of an Asteroid By sending two pulses at an asteroid and timing the difference between the lengths of time each pulse takes to reach the asteroid and return, the velocity (relative to you) can be found. When doing such calculations it is very important to remember the factor of two involved.

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