Practical No. 10: Determination of Joule’s mechanical equivalent of heat by Joule’s law.
XIV. Conclusions and Recommendations
- The experiment successfully demonstrates the conversion of electrical energy into heat energy and verifies Joule’s law.
- It is recommended to stir the water continuously for uniform temperature distribution.
XV. Practical Related Questions & Answers
Q1. Will there be any change in amount of heat produced, if direction of current is changed. Give reasons for your answer.
- Answer: No, there will be no change in the amount of heat produced.
- Reason: The heating effect of current (H = I²Rt) depends on the square of the current. Since the square of both positive and negative values is always positive, the heat produced is independent of the direction of current flow.
Q2. The work done 5000 J is equivalent to how many kcal?
- Answer:
- Formula: Heat (H) = Work done (W) / J
- Given Data: W = 5000 J, J = 4186 J/kcal
- Calculation:
- H = 5000 / 4186
- H ≈ 1.194 kcal
Q3. If amount of current passed through coil is doubled, determine the corresponding change in the heat produced.
- Answer:
- Explanation: From Joule’s law, H = I²Rt. If the current (I) is doubled (becomes 2I), the new heat produced will be (2I)² = 4I². Therefore, the heat produced will increase by four times.
Q4. Is there any change in amount of heat produced if heating element of coil is replaced by Copper (keeping the current constant). Give reasons.
- Answer: Yes, the amount of heat produced will change.
- Reason: The heat produced depends directly on resistance (H = I²Rt). If the coil is replaced by a copper wire of the same dimensions, its resistance will be much lower because copper has very low resistivity. Therefore, the heat produced will be significantly less.
Q5. State & explain Joule’s law.
- Answer: Joule’s law states that the heat (H) produced in a resistor is directly proportional to the square of the current (I) flowing through it, the resistance (R) of the resistor, and the time (t) for which the current flows.
- Mathematical expression: H = I²Rt
- Explanation: Electrical work done (W = VIt) is converted into heat. Using Ohm’s law (V = IR), this work is expressed as W = I²Rt, which appears entirely as heat energy.
Leave a Reply