Electric potential and potential energy: Class 12 practice
Potential of a point charge V = kq/r (a scalar, so add with signs). Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Coulomb's law
The idea behind electric potential and potential energy
Potential of a point charge V = kq/r (a scalar, so add with signs). Potential energy of two charges U = kq₁q₂/r. Work to move charge q through ΔV is qΔV.
Step-by-step method
- Use V = kq/r for each charge.
- Add potentials algebraically.
- U = kq₁q₂/r; W = qΔV.
Worked example 1 (Basic)
Find the potential 0.5 m from a 3 μC charge.
- V = kq/r = 9 × 10⁹ × 3 × 10⁻⁶/0.5
- = 5.400e+4 V
- Answer: 5.400e+4 V
Worked example 2 (Standard)
Find the potential energy of charges 1 μC and -4 μC placed 0.5 m apart.
- U = kq₁q₂/r
- = -7.200e-2 J
- Answer: -7.200e-2 J
Worked example 3 (Challenge)
How much work moves 2 μC through a potential difference of 174 V?
- W = qΔV = 2 × 10⁻⁶ × 174
- = 3.48e-4 J
- Answer: 3.48e-4 J
Common mistakes and misconceptions
- Treating potential as a vector
- Dropping signs of charges
Practice questions
- (Basic) Find the potential 0.1 m from a 7 μC charge.
- (Basic) Find the potential 0.5 m from a 9 μC charge.
- (Standard) Find the potential energy of charges 2 μC and -1 μC placed 0.5 m apart.
- (Standard) Find the potential energy of charges 5 μC and -1 μC placed 0.7 m apart.
- (Challenge) How much work moves 3 μC through a potential difference of 460 V?
- (Challenge) How much work moves 8 μC through a potential difference of 493 V?
Answer key with full working
- Q1: V = kq/r = 9 × 10⁹ × 7 × 10⁻⁶/0.1 → = 6.300e+5 V → Answer: 6.300e+5 V
- Q2: V = kq/r = 9 × 10⁹ × 9 × 10⁻⁶/0.5 → = 1.620e+5 V → Answer: 1.620e+5 V
- Q3: U = kq₁q₂/r → = -3.600e-2 J → Answer: -3.600e-2 J
- Q4: U = kq₁q₂/r → = -6.429e-2 J → Answer: -6.429e-2 J
- Q5: W = qΔV = 3 × 10⁻⁶ × 460 → = 1.38e-3 J → Answer: 1.38e-3 J
- Q6: W = qΔV = 8 × 10⁻⁶ × 493 → = 3.94e-3 J → Answer: 3.94e-3 J
Syllabus note
This skill is listed under "Electrostatic Potential and Capacitance" for Class 12 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
Frequently asked questions
Which chapter is electric potential and potential energy in?
"Electrostatic Potential and Capacitance", Class 12 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.