• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Is a filament lamp an ohmic resistor?

Extracts from this document...

Introduction

Is a filament lamp an ohmic resistor?

During this coursework I am investigating to find out whether a filament lamp is an ohmic resistor, an ohmic resistor is a resistor that follows ohm’s law.

image06.pngimage01.pngimage00.png

I want to get the results as accurate as possible so I shall us a digital ammeter and voltmeter and record my results to 2 decimal places.

Before I started the investigation I had to find some research. I researched 3 books to find out mainly about resistance, ohm’s law and ohmic resistors.

The first book was: -

Extension Physics by Brian Milner

“To make a bulb light up, you must out a potential difference (voltage) across it. A current can then flow through the filament of the bulb. The filament resists a current flowing though it, so we say it has a resistance”.

“We measure resistance in units called ohms. To measure a resistance you nee to know how big a current flows through it when you put a particular potential difference (P.D) across it. Then you can work out the resistance like this:

             Resistance = Potential difference (volt, V)

               (ohms,   )       Current (amperes, A)

The filament of a bulb becomes hot because it resists the current flowing through it.”

Physics for today and tomorrow, 2nd edition: tom Duncan.

Ohm’s law:

“When the same p.d. is applied across different conductors different current flow depending on how easily electrons can more in them.

...read more.

Middle

image04.png

image05.png

Method

1 The first crocodile clip is clipped to the wire at the 0cm position on the metre rule.

2.The second crocodile clip is clipped to the required position depending on the required length of wire.

3.The power supply is turned on. The voltage and current are then read off the ammeter and voltmeter, and recorded.

4.The power supply is then turned off and the second crocodile clip is moved to the next position.

The above steps are completed for each length and then the entire investigation is repeated for accuracy. I will also use digital ammeters and voltmeters for accuracy.

OBSERVATION

With reading my research I have came to a prediction that The longer the wire, the higher the resistance this is because the longer the wire, the more times the free electrons will collide with other free electrons This is because, the particles making up the metal, and any impurities in the metal. So, more energy is going to be lost in these collisions as heat.

I set out my apparatus as shown;

Using this I decided to record results I decided to simultaneously record the volts and amps to work out the resistance.

Length

Amps

Volts

Resistance(   )

15cm

3.78

0.85

0.22

30cm

2.75

1.28

0.47

45cm

2.33

1.47

0.63

60cm

2.01

1.61

0.80

75cm

1.77

1.74

0.98

90cm

1.53

1.91

1.25

100cm

1.31

1.94

1.48

image06.png

But we did not include the variable resistor at first. We placed a thin copper wire along

...read more.

Conclusion

2.

0.10

0.06

0.80

3.

0.15

0.09

0.60

4.

0.21

0.13

0.62

5.

0.33

0.20

0.63

6.

0.67

0.41

0.61

Length

Amps

Volts

Resistance()

1. 60cm

0.08

0.06

0.75

2.

0.10

0.08

0.80

3.

0.14

0.11

0.79

4.

0.22

0.18

0.82

5.

0.38

0.30

0.79

6.

0.62

0.44

0.79

Length

Amps

Volts

Resistance()

1. 75cm

0.08

0.09

1.13

2.

0.11

0.11

1.00

3.

0.14

0.15

1.07

4.

0.21

0.21

1.00

5.

0.31

0.31

1.00

6.

0.50

0.50

1.00

Length

Amps

Volts

Resistance()

1. 90cm

0.08

0.17

2.13

2.

0.10

0.20

2.00

3.

0.15

0.30

2.00

4.

0.25

0.46

1.84

5.

0.40

0.57

1.43

6.

0.86

1.27

1.48

Length

Amps

Volts

Resistance()

1. 100cm

0.09

0.12

1.30

2.

0.12

0.16

1.30

3.

0.16

0.22

1.38

4.

0.25

0.34

1.36

5.

0.48

0.64

1.30

6.

0.95

1.29

1.36

Conclusions

Having performed the investigation, the following conclusion were drawn:

As predicted, an increase in length resulted in an increased resistance

Evaluation

Looking at the graph i can see that ohms law does happen with the variable resistor

If thought that Ohm’s Law applies, and then another possible explanation could be that at some points properly in the lower lengths, the wire was not allowed to cool completely so that the temperature was higher for that measurement. Whilst unlikely this would cause a higher resistance as explained previously. However, it is now known, after researching the metal alloy “constantan,” that the resistivity which is the electrical resistance of a conductor of particular area and length of this alloy is not affected by temperature. So, in these experiments Ohm’s Law does not apply.

...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. Electrical Properties of a Filament Lamp - Does a Filament Lamp Obey Ohm's Law?

    Biblioraphy www.grc.nasa.gov www.gcse.com/ohm.htm www.bbc.co.uk/schools/gcsebitesize/physics/ Letts GCSE Physics Britannica Encyclopaedia Variables I am going to change the resistance and monitor the voltage and current. I am going to use the voltage as a basis for the experiment and for every 1volt increase I will record the current reading.

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

    When the current of the light bulb increases form 27.5 MA to 60 MA, the resistance of the LDR decrease as well, so the current increase. Evaluation From my results table and graph, I can see that my results that I collected are quite reliable and accurate.

  1. Investigation into the resistance of a filament lamp.

    because the vibrating ions obstruct electrons at high temperature so therefore that increase the resistance) > The impurities of a metal, the resistance of a impure metal is greater than that of a pure metal. Current Definition: Current is the movement of electrical charge - the flow of electrons through the electronic circuit.

  2. resistivity if a nichrome wire

    the resistance I simply added the % error of the current to the % error of the voltage. To work out the resistance I used ohms law: V=IR. I however rearranged this equation in order to make the resistance the subject. This therefore becaie R= V/I For example: (0.100m length)

  1. Characteristics of Ohmic and non-Ohmic Conductors.

    The energy pushes the electrons farther away from the nucleus of the atoms. As the electrons fall back, they give off photons,which are little bits of light. Current (I) V I Voltage (V) In a filament lamp, the graph of I against V becomes less and less steep as the current increases from zero.

  2. Characteristics of Ohmic and Non-Ohmic Conductors.

    As more current flows through a thermistor, the kinetic energy of the electrons increases and they flow through the material with a greater speed. As this happens, the current increases and the resistance, therefor, decreases. The V-I graph of a thermistor can be seen below.

  1. Investigating Ohms law

    by a large scale ammeter, therefore a digital ammeter is used to measure the small current in the light bulb and thermistor.

  2. Investigate the current - voltage relationship for a resistor and filament lamp. To determine ...

    * Again, readings are taken from the voltmeter and ammeter as the variable resistor is moved along. * Readings are recorded in another table. When the variable resistor has reached the end or there are sufficient results, the current can be directed backwards again for negative readings.

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