Electric field, potential and energy

Topic 9.3 (AHL)

Remember?• Define potential difference (voltage).

Remember?• Define potential difference (voltage).

• Amount of electrical energy converted to heat when a charge flows through a resistor.

EPE• Draw the electric field lines.

EPE• If a positive charge was placed in the plate.

Which direction will it move?

EPE• Which direction will require you to do some

work?• When you do this work will it increase its KE

or PE?

EPE• What’s the direction of the electric force on

positive charge? State equation

EPE• F= Eq, then to move the positive charge from

negative to positive plate, we need to apply equal and opposite force.

EPE• Therefore the work done = Fd = Eqd = Eqh• We increased the electrical PE (EPE)

Electric potential• Where will you have the greatest electrical

potential energy?• Can you define electric potential at a point?

(remember gravitational potential and change the terms)

Electric potential• Where will you have the greatest electrical

potential energy?• Can you define electric potential at a point?

Work done per unit charge taking a small positive test charge from infinity to a point.

• Unit?

Electric potential• Where will you have the greatest electrical

potential energy?• Can you define electric potential at a point?

Work done per unit charge taking a small positive test charge from infinity to a point.

• Unit? JC-1 or Volts• Potential is a scalar quantity• Reminder: at infinity you have zero potential

(like gravitational)

Electric potential• Where will you have zero potential?• Greatest potential?• Equal potential (equipotential)

Electric potential• Where will you have zero potential? bottom• Greatest potential? Top • Equal potential (equipotential)

Electric potential• Equation for change in potential?

Electric potential• Equation for change in potential?

Electric potential• Draw field lines and equipotential lines for the

a positive test charge.

Electric potential• Draw field lines and equipotential lines for the a

positive test charge.(red: equipotential line, black: field lines)

Electric potential• Draw field lines and equipotential lines when two

positive charges are brought close to each other.

Electric potential• Draw field lines and equipotential lines when two

positive charges are brought close to each other.• Try other patterns on simulation.

Force VS distance graph

• Force more or less if two positive charges get closer to each other? Predict shape of graph

Force VS distance graph

• Force more or less if two positive charges get closer to each other? Predict shape of graph

gravitational

electrical

Force VS distance graph

• What will the area represent? Equation

electrical

Force VS distance graph

• What will the area represent? Equation

electrical

Potential vs distance• How will the graph look like for a positive

charge?

Potential vs distance• Potential inside positive sphere is constant• What will the tangent represent?

Potential vs distance• What will the tangent represent?

• -E (since E will be positive)

x

E and V graphs

E and V graphs

Wells and hills• In gravitational we saw the wells

Wells and hills• In electrical it can be both wells and hills.

• Well is potential is decreasing as you approach ? charge

• Hill if potential increasing as you approach ? charge

Wells and hills• In electrical it can be both wells and hills.

• Well is potential is decreasing as you approach negative charge

• Hill if potential increasing as you approach positive charge

A combination of positive and negative charge is called a dipole

Addition of potential• Potential is scalar therefore add without

considering direction

+ –

P

Questions 30,31 P.203• Which charge is positive which is negative and explain

• If a positive charge is placed at A, would it move? In which direction if yes

• In which point is the field strength greatest?

Questions 30,31 P.203

comparison