Charge, current and number of electrons: Class 10 practice
Current is the rate of flow of charge: I = Q/t. Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Units of time
The idea behind charge, current and number of electrons
Current is the rate of flow of charge: I = Q/t. One electron carries 1.6 × 10⁻¹⁹ C, so the number of electrons n = Q/e.
Step-by-step method
- Q = I × t (t in seconds).
- n = Q ÷ 1.6 × 10⁻¹⁹.
- Rearrange for I or t as needed.
Worked example 1 (Basic)
A current of 5.5 A flows for 4 s. How much charge passes?
- Q = 5.5 × 4
- Answer: 22 C
Worked example 2 (Standard)
4 A flows for 24 minutes. How many electrons pass a point?
- Q = 4 × 1440 = 5760 C
- n = 5760/1.6 × 10⁻¹⁹ = 3.600e+22
- Answer: 3.600e+22
Worked example 3 (Challenge)
240 C passes through a lamp in 2 minutes. Find the current.
- I = 240/120
- Answer: 2 A
Common mistakes and misconceptions
- Leaving time in minutes
- Multiplying by e instead of dividing
Practice questions
- (Basic) A current of 6 A flows for 25 s. How much charge passes?
- (Basic) A current of 3.5 A flows for 10 s. How much charge passes?
- (Standard) 3 A flows for 4 minutes. How many electrons pass a point?
- (Standard) 4 A flows for 9 minutes. How many electrons pass a point?
- (Challenge) 11700 C passes through a lamp in 30 minutes. Find the current.
- (Challenge) 600 C passes through a lamp in 5 minutes. Find the current.
Answer key with full working
- Q1: Q = 6 × 25 → Answer: 150 C
- Q2: Q = 3.5 × 10 → Answer: 35 C
- Q3: Q = 3 × 240 = 720 C → n = 720/1.6 × 10⁻¹⁹ = 4.500e+21 → Answer: 4.500e+21
- Q4: Q = 4 × 540 = 2160 C → n = 2160/1.6 × 10⁻¹⁹ = 1.350e+22 → Answer: 1.350e+22
- Q5: I = 11700/1800 → Answer: 6.5 A
- Q6: I = 600/300 → Answer: 2 A
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
- Heating effect of current (Joule's law)
- Mixed series–parallel circuits
- Power rating, current and fuse choice
- 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 charge, current and number of electrons 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.