Panitia Fizik SMJK Yu Hua Kajang FM5 Peka 2013

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PEKA: Ohms Law

Aim :

1. To investigate the relationship potential difference and current for

a constantan wire

2. To determine the resistance per meter of a constantan wire

3. To investigate the relationship between potential difference and

current across a filament bulb

Question suitable for scientific investigation

What is the effect of changing the current in the circuit with respect to the

voltage over the constantan wire

Inference : As the current increases, the potential difference will increase

Variables:

Manipulated variable : Current in the circuit

Responding variable: Potential difference over the constantan wire

Fixed variable : The resistance of the wire

Hypothesis : Current is directly proportional to the voltage if the resistance

is kept constant

Apparatus and material :

4 units of 1.5V Dry Cell (Type D), Battery Holder, Rheostat, Voltmeter,

Ammeter, Switch, connecting wires, ½ m constantan wire, 3V Bulb and bulb

holder

Panitia Fizik SMJK Yu Hua Kajang FM5 Peka 2013

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A

V

BatterySwitch

Ammeter

Voltmeter

Constantan Wire

Rheostat

A B

Procedure :

1. Setup the circuit diagram as shown above.

2. Place a 0.5m constantan wire across points A and B

3. The circuit is switched on

4. The rheostat is adjusted slowly until the ammeter shows a reading of

0.2 A. Record the voltmeter reading.

5. The ammeter reading I and the voltmeter reading V are recorded

6. Step 4 is repeated using a current of 0.4 A, 0.6 A, 0.8 A and 1.0 A

respectively.

7. All ammeter and voltmeter reading are recorded

8. Replace the constantan wire with the bulb provided

9. Repeat steps 4 - 7

10. Draw a suitable graph of voltage V against current I for the constantan

wire and bulb.

11. Determine the gradient of the graph for the constantan wire

Panitia Fizik SMJK Yu Hua Kajang FM5 Peka 2013

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12. Determine the resistance of the constantan wire

13. Draw a conclusion for the relationship between V and I for the bulb

14. From the graph, determine a resistance of the bulb when the bulb is

not glowing

15. From the graph, determine a resistance of the bulb when the bulb is

glowing/lighted

Data Tabulation :

Ammeter Reading

I/A

Voltmeter Reading/ V

Constantan wire

Voltmeter Reading/ V

Bulb

0.2

0.4

0.6

0.8

1.0

Graph:

(i) Graph of Voltage (V) against Current (I) for constantan wire

Voltage / V

Current / I

V

I

Panitia Fizik SMJK Yu Hua Kajang FM5 Peka 2013

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(ii) Graph of Voltage (V) against Current (I) for a filament bulb

Voltage / V

Current / I

R1

R2

From the graph :

The gradient can be calculated by

R = V/I

Conclusion :

1) For a fixed resistance, the potential difference cross an Ohmic

conductor is directly proportional to the current passing through it.

R = V/I

2) Resistance of the constantan wire is __________ Ω/m

3) Resistance of the bulb when it is not glowing

R1 = V1/I 1

Panitia Fizik SMJK Yu Hua Kajang FM5 Peka 2013

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4) Resistance of the bulb when it is glowing

R2 = V2/ I2

Precautions :

1.

2.