Potential difference is defined as the work done to move a unit charge from one point to the other. The SI unit of potential difference is volt. Electromotive force is defined as the force that distributes the equilibrium of free-flowing electrons. Below is an experiment to study the dependence of the potential difference across a resistor with current-carrying I.
To study the dependence of potential difference (V) across a resistor on the current (I) passing through it and determine its resistance. Also, plot a graph between V and I.
What is Ohm’s law?
In an electric circuit, the potential difference V across the metallic wire is directly proportional to the current flowing through the circuit with a constant temperature. This is known as Ohm’s law.
V∝I. ∴ V=IR.
What are the factors affecting resistance?
Following are the factors affecting resistance:
- The nature of the resistor.
- With an increase in length, the resistance also increases. So length also affects the resistance.
- With an increase in the cross-sectional area, the resistance decreases. So cross-sectional area of the wire affects the resistance.
Following is the list of materials required for this experiment:
- A battery
- An insulated copper wire
- A key
- An ammeter
- A voltmeter
- A rheostat
- A resistor
- A piece of sandpaper
- Arrange the devices as shown in the circuit diagram.
- Connect the devices with the connecting wires keeping the key open.
- The positive terminal of the battery should be connected to the positive terminal of the ammeter.
- Before connecting the voltmeter in the circuit, check for +ve and -ve terminals.
- Check for ammeter and voltmeter reading once the circuit is connected and also adjust the slider of rheostat after inserting the key.
- For current I and voltmeter V, record three different readings using a slider.
- Record the observations in the observation table.
- Using the formula R=V/I, calculate the resistance.
- To plot the graph between V and I, take V on the x-axis and I on the y-axis.
- For pure metals, resistance increases with an increase in temperature.
i) Least count of ammeter and voltmeter
|Sl.no||Ammeter (A)||Voltmeter (V)|
|1||Range||0-0.5 A||0-0.1 V|
|2||Least count||0.01 A||0.01 V|
|3||Zero error (e)||0||0|
ii) For the reading of ammeter and voltmeter
|Sl.no||Current in Ampere (I)
|Potential difference in volts (V)
|Resistance in ohms
R = V/I (Ω)
- For all the three readings, the R-value is the same and constant.
- The ratio of potential difference V and current I is the resistance of a resistor.
- With the help of the graph between V and I, Ohm’s law is verified as the plot is a straight line.
- Thick copper wires are used as connecting wires and using sandpaper, their insulation is removed.
- To avoid external resistance, the connections should be tight.
- The connections should be as per the circuit diagram and should be approved by the teacher before conducting the experiment.
- The current should enter from the positive terminal and exit from the negative terminal of the ammeter and should be connected in series with the resistor.
- Resistor and voltmeter should be connected in parallel.
- The least count of ammeter and voltmeter should be recorded properly.
- When there is no current flow, the pointers of ammeter and voltmeter should be at zero.
- To avoid unnecessary heating in the circuit, the current should be passed for a short time.
Q1. Define electric current.
Ans: Electric current is defined as the rate of flow of electric charge in a conductor.
- I is the current in amperes
- Q is the electric charge in coulombs
- t is the time in seconds
Q2. What is the value of charge in 1 electron?
Ans: The value of charge in 1 electron is 1.6×10-19C.
Q3. What is coulomb?
Ans: Coulomb is an SI unit of electric charge and is defined as the amount of charge present in 6.25×1018 electrons.
Q4. What is 1 volt?
Ans: 1 volt is defined as the work done in 1 Joule to move a charge of 1 Coulomb from one point to the other than the potential difference is 1 volt.
Q5. What is 1 ohm?
Ans: 1 ohm is defined as the resistance offered by an object when one ampere current flows through an object with a potential difference of one volt.
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