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Transcript
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