Download Electric field, potential and energy

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
electrical
9.2 GRAVITATIONAL POTENTIA
! If
gravitational
we plot the gravitational force a
! Can
you explain the graph and wh
Force VS distance
graph
• What will the area represent? Equation
electrical
Force VS distance
graph
• What will the area represent? Equation
electrical
kQq
W =
r
W = Vq
kQ
V = W /q =
r
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
L AND POTENTIAL WALLS
Wells and hills
uipotential lines, equipotential
• 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
+
kQ1 kQ2
V=
+
r1
r2
–
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