Heating effect of current (Joule's law): Class 10 practice
Heat produced H = I²Rt = VIt = V²t/R. Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Ohm's law
- Squares
The idea behind heating effect of current (joule's law)
Heat produced H = I²Rt = VIt = V²t/R. Doubling current makes four times the heat. Fuses and heaters work on this effect.
Step-by-step method
- Choose the form that matches the data.
- Use SI units (A, Ω, s).
- Calculate H in joules.
Worked example 1 (Basic)
A current of 3 A flows through 22 Ω for 4 min. Find the heat produced.
- H = I²Rt = 3² × 22 × 240
- = 47520 J
- Answer: 47520 J
Worked example 2 (Standard)
A 75 V supply drives current through a 25 Ω heater for 360 s. Find the heat produced.
- H = V²t/R = 75² × 360/25
- = 81000 J
- Answer: 81000 J
Worked example 3 (Challenge)
A 8 Ω resistor carries 2 A for 540 s. If the current becomes 4 A, find the new heat and how many times larger it is.
- H ∝ I²: 2² = 4 times
- New H = 4 × 17280 = 69120 J
- Answer: 69120 J (4 times)
Common mistakes and misconceptions
- Using minutes instead of seconds
- Forgetting to square I
Practice questions
- (Basic) A current of 3 A flows through 13 Ω for 9 min. Find the heat produced.
- (Basic) A current of 2 A flows through 43 Ω for 6 min. Find the heat produced.
- (Standard) A 8 V supply drives current through a 8 Ω heater for 60 s. Find the heat produced.
- (Standard) A 198 V supply drives current through a 33 Ω heater for 60 s. Find the heat produced.
- (Challenge) A 30 Ω resistor carries 3 A for 180 s. If the current becomes 9 A, find the new heat and how many times larger it is.
- (Challenge) A 41 Ω resistor carries 4 A for 300 s. If the current becomes 12 A, find the new heat and how many times larger it is.
Answer key with full working
- Q1: H = I²Rt = 3² × 13 × 540 → = 63180 J → Answer: 63180 J
- Q2: H = I²Rt = 2² × 43 × 360 → = 61920 J → Answer: 61920 J
- Q3: H = V²t/R = 8² × 60/8 → = 480 J → Answer: 480 J
- Q4: H = V²t/R = 198² × 60/33 → = 71280 J → Answer: 71280 J
- Q5: H ∝ I²: 3² = 9 times → New H = 9 × 48600 = 437400 J → Answer: 437400 J (9 times)
- Q6: H ∝ I²: 3² = 9 times → New H = 9 × 196800 = 1771200 J → Answer: 1771200 J (9 times)
Syllabus note
This skill is listed under "Electricity" for Class 10 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
- Electricity chapter notes (Class 10)
- Ohm's law and resistors in series and parallel
- Electric power and energy consumption
- Resistivity and resistance of a wire
- Mixed series–parallel circuits
- Power rating, current and fuse choice
- Charge, current and number of electrons
- Lens formula and magnification
- Mirror formula and magnification
- Refractive index and speed of light
- Power of a lens and lens combinations
- All Class 10 practice
Frequently asked questions
Which chapter is heating effect of current (joule's law) in?
"Electricity", Class 10 Physics (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.