⚡ Ohm's Law Experiment

Verify V = IR and Calculate Resistance with Interactive Circuit

✅ FREE Experiment • 📊 V-I Graph Plotting • 🎓 NEB Class 11 Practical

Interactive Circuit

Adjust voltage and watch current flow through the resistor!

Experiment Controls

Range: 0.5V - 12V (Battery voltage)

Choose different resistor values

Account for wire resistance

Real-Time Measurements

Voltage (V)
3.0
Volts
Current (I)
0.136
Amperes
Resistance (R)
22.0
Ohms (Ω)
Power (P)
0.41
Watts

Observation Table

S.No. Voltage (V)
Volts		 Current (I)
Amperes		 Resistance (R)
R = V/I (Ω)		 V/I Ratio
No observations yet. Measure current and click "Add to Table"

📊 Analysis

Mean Resistance (R) = 0.00 Ω

Expected value = 22.0 Ω

Percentage error = 0.00%

✓ V/I ratio is constant (Ohm's Law verified)

📈 Voltage vs Current Graph

The straight line through origin verifies Ohm's Law (V ∝ I)

📚 Theory & Concepts

What is Ohm's Law?

Ohm's Law states that the current flowing through a conductor is directly proportional to the potential difference (voltage) across it, provided the physical conditions (temperature, pressure) remain constant.

Mathematical Expression

V = IR

Where:
• V = Potential difference (Voltage) in Volts (V)
• I = Current in Amperes (A)
• R = Resistance in Ohms (Ω)

Alternative Forms

From V = IR, we can derive:

I = V/R     and     R = V/I

Proportionality Statement

At constant temperature and pressure:

V ∝ I     (V/I = constant = R)

This means if we plot a graph of voltage (V) on Y-axis versus current (I) on X-axis, we get a straight line passing through the origin. The slope of this line is the resistance R.

Resistance

Resistance is the property of a conductor to oppose the flow of electric current through it. It depends on:

R = ρL/A

Where ρ (rho) is the resistivity of the material.

Power Dissipation

When current flows through a resistor, electrical energy is converted to heat. The power dissipated is:

P = VI = I²R = V²/R

Power is measured in Watts (W).

Ohmic vs Non-Ohmic Conductors

Ohmic conductors: Conductors that obey Ohm's Law (metals, carbon resistors). Their V-I graph is a straight line through origin.

Non-Ohmic conductors: Conductors that do not obey Ohm's Law (diodes, transistors, filament bulbs). Their V-I graph is not a straight line.

Key Points

🔬 Procedure

  1. Select a resistor value (e.g., 22 Ω) from the dropdown
  2. Choose wire resistance (ideal = 0 Ω for simplicity)
  3. Set the voltage to a low value (e.g., 1.0 V) using the slider
  4. Click "Measure Current" to calculate the current flowing through the circuit
  5. Observe the ammeter reading showing the current in Amperes
  6. Note the voltage, current, and calculated resistance values
  7. Click "Add to Table" to record this observation
  8. Increase the voltage in steps (2V, 3V, 4V, 5V, 6V...)
  9. Repeat steps 4-7 for each voltage value (at least 6-8 readings)
  10. Observe that as voltage increases, current also increases proportionally
  11. Calculate V/I ratio for each reading - it should be constant (= R)
  12. Click "Plot V-I Graph" to visualize the voltage-current relationship
  13. Verify that the graph is a straight line passing through origin
  14. Calculate the mean resistance from all observations
  15. Compare with the actual resistor value and find percentage error

💬 Viva Questions & Answers

Q1: State Ohm's Law.
Ohm's Law states that the current flowing through a conductor is directly proportional to the potential difference across it, provided the physical conditions (temperature, pressure) remain constant. Mathematically: V = IR or V ∝ I.
Q2: What is resistance?
Resistance is the property of a conductor that opposes the flow of electric current through it. It is measured in Ohms (Ω). Resistance depends on the material, length, cross-sectional area, and temperature of the conductor.
Q3: What is the SI unit of resistance?
The SI unit of resistance is Ohm, denoted by the symbol Ω (Greek letter omega). One Ohm is defined as the resistance of a conductor when a potential difference of 1 Volt causes a current of 1 Ampere to flow through it.
Q4: How do you verify Ohm's Law experimentally?
Ohm's Law is verified by plotting a graph of voltage (V) versus current (I). If we get a straight line passing through the origin, it proves V ∝ I, thus verifying Ohm's Law. Additionally, the V/I ratio should remain constant for all readings, equal to the resistance R.
Q5: What does the slope of V-I graph represent?
The slope of the voltage-current (V-I) graph represents the resistance (R) of the conductor. Since V = IR, the slope = V/I = R. A steeper slope indicates higher resistance, while a gentler slope indicates lower resistance.
Q6: What are Ohmic and Non-Ohmic conductors?
Ohmic conductors obey Ohm's Law and have a linear V-I relationship (straight line graph). Examples: metals, carbon resistors. Non-Ohmic conductors do not obey Ohm's Law and have non-linear V-I graphs. Examples: diodes, transistors, filament bulbs, thermistors.
Q7: What factors affect resistance of a conductor?
Resistance depends on: (1) Length - R ∝ L (longer wire has more resistance), (2) Cross-sectional area - R ∝ 1/A (thicker wire has less resistance), (3) Material - different materials have different resistivities, (4) Temperature - resistance generally increases with temperature for metals.
Q8: What is the formula for resistance in terms of resistivity?
The resistance R is given by R = ρL/A, where ρ (rho) is the resistivity of the material, L is the length of the conductor, and A is its cross-sectional area. Resistivity is a material property measured in Ohm-meters (Ω·m).
Q9: What is the function of an ammeter in the circuit?
An ammeter is used to measure the current flowing through the circuit. It is always connected in series with the circuit. An ideal ammeter has zero resistance so it doesn't affect the circuit current. The reading is given in Amperes (A) or milliamperes (mA).
Q10: What is the function of a voltmeter in the circuit?
A voltmeter is used to measure the potential difference (voltage) across a component. It is always connected in parallel with the component. An ideal voltmeter has infinite resistance so it draws no current from the circuit. The reading is given in Volts (V).
Q11: Why must temperature be kept constant in Ohm's Law?
Temperature must be kept constant because resistance of most conductors changes with temperature. For metals, resistance increases with temperature. If temperature varies during the experiment, the V/I ratio will not remain constant, and Ohm's Law will not be verified accurately.
Q12: What is electric power and how is it related to Ohm's Law?
Electric power is the rate at which electrical energy is consumed or dissipated. It is given by P = VI. Using Ohm's Law (V = IR), we can write P = I²R or P = V²/R. Power is measured in Watts (W). This power is dissipated as heat in the resistor.
Q13: What are the sources of error in this experiment?
Main sources of error: (1) Zero error in ammeter and voltmeter, (2) Resistance of connecting wires (not negligible), (3) Heating of resistor causing resistance change, (4) Parallax error in reading meters, (5) Internal resistance of battery, (6) Loose connections in circuit.
Q14: Why does the V-I graph pass through the origin?
The V-I graph passes through the origin because when voltage is zero, current is also zero (from I = V/R, if V = 0, then I = 0). This shows the direct proportionality between voltage and current. If the graph doesn't pass through origin, it indicates systematic error in the experiment.
Q15: What are practical applications of Ohm's Law?
Applications include: (1) Designing electrical circuits and selecting proper resistors, (2) Calculating power consumption in appliances, (3) Determining wire thickness for electrical installations, (4) Troubleshooting electrical faults, (5) Designing voltage dividers and current limiters, (6) Understanding power transmission losses, (7) Battery selection for circuits.