Edexcel A Level (IAL) Physics-4.16 Electric Field & Potential- Study Notes- New Syllabus
Edexcel A Level (IAL) Physics -4.16 Electric Field & Potential- Study Notes- New syllabus
Edexcel A Level (IAL) Physics -4.16 Electric Field & Potential- Study Notes -Edexcel A level Physics – per latest Syllabus.
Key Concepts:
- know and understand the relation between electric field and electric potential
Relationship Between Electric Field and Electric Potential
Electric field and electric potential are closely related concepts used to describe electric phenomena. The electric field describes force effects, while electric potential describes energy effects.
Electric Potential (Reminder)
Electric potential at a point is defined as the work done per unit charge in bringing a positive test charge from infinity to that point.
\( V = \dfrac{W}{Q} \)
- \( V \) = electric potential (V)
- \( W \) = work done (J)
- \( Q \) = charge (C)
How Electric Field and Potential Are Related
The electric field is related to how quickly the electric potential changes with distance.
Definition:
Electric field strength is the potential gradient.
\( E = -\dfrac{\Delta V}{\Delta x} \)
- \( E \) = electric field strength (V m⁻¹ or N C⁻¹)
- \( \Delta V \) = change in electric potential (V)
- \( \Delta x \) = distance moved in the direction of the field (m)
Negative sign:
- Electric field points in the direction of decreasing potential.
- Potential always decreases in the direction of the electric field.
Uniform Electric Field
In a uniform electric field (e.g. between parallel plates):
\( E = \dfrac{V}{d} \)
- \( V \) = potential difference between plates (V)
- \( d \) = separation between plates (m)
This is a special case of the potential gradient equation.
Physical Meaning of the Relationship
- A strong electric field means potential changes rapidly with distance.
- A weak electric field means potential changes slowly with distance.
- Electric field lines point from higher potential to lower potential.
Connection with Force and Energy
The force on a charge in an electric field is:
\( F = EQ \)
The change in electric potential energy is:
\( \Delta E = Q\Delta V \)
This shows how force, field, and energy are linked.
Key Summary
- Electric field is the spatial rate of change of electric potential.
- Field direction is from high potential to low potential.
- Electric potential describes energy per unit charge.
- Electric field describes force per unit charge.
Example (Easy)
A potential difference of \( 300\ \mathrm{V} \) exists across two parallel plates separated by \( 0.020\ \mathrm{m} \). Find the electric field strength.
▶️ Answer / Explanation
\( E = \dfrac{V}{d} = \dfrac{300}{0.020} = 1.5\times10^{4}\ \mathrm{V\,m^{-1}} \)
Example (Medium)
The electric field strength between two plates is \( 2.0\times10^{4}\ \mathrm{V\,m^{-1}} \). Calculate the potential difference across the plates if they are \( 0.015\ \mathrm{m} \) apart.
▶️ Answer / Explanation
\( V = Ed = (2.0\times10^{4})(0.015) = 300\ \mathrm{V} \)
Example (Hard)
Explain why electric field lines are always perpendicular to equipotential surfaces.
▶️ Answer / Explanation
- Equipotential surfaces have constant potential.
- No work is done moving along an equipotential.
- Electric field acts in the direction of maximum decrease of potential.
- This direction is perpendicular to equipotential surfaces.