12th Physics, Chapter 12th, Punjab text Book

1. ELECTRIC POTENTIAL
Dr. Nadeem Khalid
AL-AQSA ACADEMY, LAHORE

2. • Electric potential
• Electric potential is a pushing force
ELECTRIC POTENTIAL
+
+ +
+
Low potential
High potential

3. • Definition
• The work done in carrying a unit positive charge from one point to the other
while keeping the charge in electrostatic equilibrium.
• Formula
• ∆𝑉 =
𝑊
𝑞
• Nature
• Scalar quantity
ELECTRIC POTENTIAL DIFFERENCE

4. • Unit
• Volt (V)
• Volt
• Definition
• If one joule work is done in carring a unit positive charge from one point to another
keeping electrostatic equilibrium then potential difference is said to be on volt
• 1 volt =
1 𝑗𝑜𝑢𝑙𝑒
1 𝑐𝑜𝑢𝑙𝑜𝑚𝑏
ELECTRIC POTENTIAL DIFFERENCE

5. • Explanation
• q0 = unit positive charge in a electric field
• VA = potential at point A
• VB = potential at point B
• WAB = work done in moving charge from A to B
• ∆𝑉 = VA - VB =
WAB
q0
ELECTRIC POTENTIAL DIFFERENCE

6. • Electric potential energy and work
• q0 = unit positive charge in a magnetic field
• UA = electric potential energy at point A
• UB = electric potential energy at point B
• WAB = work done in moving charge from A to B
• ∆𝑈 = UB - UA = WAB
ELECTRIC POTENTIAL DIFFERENCE

7. • Electric potential difference between two points can also be defined
as difference of electric potential energy per unit charge
• ∆𝑉 = VA - VB =
WAB
q0
…….(A)
• ∆𝑈 = UB - UA = WAB …….(B)
• ∆𝑉 =
∆𝑈
q0
• Relation between ∆𝑽 & ∆𝑼
• ∆𝑈 = q0∆𝑉
ELECTRIC POTENTIAL DIFFERENCE IN
TERM OF POTENTIAL ENERGY

8. • Absolute electric potential at a point can be defined as the work done
in bringing a unit positive charge from infinity to that point keeping
electrostatic equilibrium
• ∆𝑉 =
WAB
q0
• VB - VA =
WAB
q0
• VA = point a is at infinity means out side the electric field so, VA = 0
• VB =
WAB
q0
• In general
• V =
WAB
q0
ABSOLUTE/ELECTRIC POTENTIAL

9. • Definition
• It is unit of energy and definied as the amount of energy acquired or lost by
an electron as it traverse through a potential defference of one volt
• Value
• 1eV = 1.6 × 10-19 J
• Explanation
• ∆𝑈 = q0∆𝑉
• ∆𝑈 = e ∆𝑉
• ∆𝑈 =(1.6 × 10−19) × 1𝑉
• ∆𝑈 =1.6 × 10−19 J
ELECTRON VOLT

11. ANSWER: A
PRACTICE TEST
∆𝑉 =
𝑊
𝑞

12. ANSWER: D
PRACTICE TEST
∆𝑈 = q0∆𝑉

14. ELECTRIC FIELD AS A
POTENTIAL GRADIENT

15. • Potential gradient
• Maximum value of rate of change electric potential in magnitude and
direction with respect to distance is known as potential gradient.
• It is always along the direction of electric field
• Mathematical form
• E = -
∆𝑉
∆𝑟
ELECTRIC FIELD AS A
POTENTIAL GRADIENT

16. • Explanation and derivation
• Two oppositely charged parallel plates
• E is uniform electric field between them
• VA potential at point A
• VB potential at point B
• ∆𝑽 is potential difference between them
• ∆𝑉 = VB – VA
• We know that
• ∆ V =
WAB
q0
• ∆ V =
F.d
q0
• ∆ V =
q0Ed
q0
W = F . d
E =
𝑭
𝒒
F = qE
ELECTRIC FIELD AS A
POTENTIAL GRADIENT

17. • Since the movement of charge is against the direction E so,
• ∆ V = -
q0Ed
q0
• ∆ V = - Ed
• E = -
∆ V
d
• If the plates A and B are separated by very small distance ∆𝑟 then above
equation becomes
• E = -
∆ V
∆𝑟
W= fd cos𝜽
W= fd cos(180)
W= fd cos(-1)
W= -fd
ELECTRIC FIELD AS A
POTENTIAL GRADIENT

18. COMPARISON OF GRAVITATIONAL
AND ELECTRIC FORCE

19. • Comparison include both
• Dissimilarities
• Similarities
•Similarities
• Both are conservative forces
• Both obey inverse square law
• Both obey superposition principal
Conservative force
Work done is
independent of path
The net response caused
by two or more stimuli is
the sum of the responses
that would have been
caused by each stimulus
individually.
COMPARISON OF GRAVITATIONAL
AND ELECTRIC FORCE

20. Electric force
• Fe = K { q1q2/r2}
• Constant value much greater
• K = 9 × 109Nm2/C2
• Stronger
• Attractive as well as repulsive
• Medium dependent
• Short range
• Can be shielded
Gravitational force
• Fg = G { m1m2/r2}
• Constant value much smaller
• G = 6.673 × 10-11Nm2/Kg2
• Weaker force
• Only attractive
• Not dependent upon medium
• Long ranged
• Can not be shielded
COMPARISON

22. PRACTICE TEST
ANSWER: B
E = -
∆𝑉
∆𝑟

23. PRACTICE TEST
ANSWER: A

25. ELECTRIC POTENTIAL AT A
POINT DUE TO POINT CHARGE

26. What is electric potential? Drive a relationship for
the electric potential at a point due to a point
charge?

27. ELECTRIC POTENTIAL AT A
POINT DUE TO POINT CHARGE

28. ELECTRIC POTENTIAL AT A
POINT DUE TO POINT CHARGE

29. ELECTRIC POTENTIAL AT A
POINT DUE TO POINT CHARGE

31. PRACTICE TEST
ANSWER: A
W = f.d
W= qEd

32. PRACTICE TEST
ANSWER: D
V =
1
𝟒𝝅𝝐
𝒒
𝒓