Induced Potential
In this lesson we learn about induced potential.
IN THIS LESSON:
Induced potential
Concept explained
Visualising the process
Click the image to enlarge it.
Practice Questions
Question 1: What two main components are required to produce an induced potential difference?
Answer: A conductor (like a wire or coil) and a magnetic field (from a magnet).
Answer Walkthrough: You need a conducting material to hold the charge carriers (electrons) and a magnetic field to act on them.
Question 2: What crucial action must happen between the magnet and the wire for a potential difference to be produced?
Answer: There must be relative motion between them. Either the magnet or the wire must be moving.
Answer Walkthrough: If both are stationary, nothing happens. The movement is key to inducing a potential.
Question 3: During this motion, what is happening to the magnetic field lines and the wire?
Answer: The wire is cutting through the magnetic field lines.
Answer Walkthrough: As the wire moves through the field, it passes through the imaginary lines of force, and this 'cutting' action is what induces the voltage.
Question 4: If you place a magnet inside a coil of wire but keep both perfectly still, what happens to the potential difference across the coil?
Answer: Nothing. The induced potential difference will be zero.
Answer Walkthrough: There is no relative motion, so no field lines are being cut.
Question 5: When a wire cuts magnetic field lines, what is produced across the ends of the wire?
Answer: A potential difference (or voltage).
Answer Walkthrough: This is the work done per unit charge, which pushes electrons along the wire.
Question 6: What is this potential difference called?
Answer: An induced potential difference or induced voltage.
Answer Walkthrough: The term 'induced' means it is created by this specific process, not from a battery.
Question 7: If the wire is part of a complete (closed) circuit, what will flow through it when a potential difference is induced?
Answer: An induced current.
Answer Walkthrough: A potential difference is necessary to drive a current, but the circuit must be complete for the current to flow.
Question 8: Does it matter whether you move the magnet and keep the coil still, or move the coil and keep the magnet still?
Answer: No, it is the relative motion between the two that matters. The effect is the same.
Answer Walkthrough: The physics depends on how the wire moves relative to the field, not on which component is doing the moving.
Question 9: What happens to the induced potential difference if you move the magnet and the wire in the same direction and at the same speed?
Answer: The induced potential difference will be zero because there is no relative motion.
Answer Walkthrough: In this case, the wire is not cutting through the field lines.
Question 10: What happens to the induced current if you push the North pole of a magnet into a coil and then pull it back out again?
Answer: The current will flow in one direction when you push it in and then reverse direction when you pull it out.
Answer Walkthrough: The direction of the induced current depends on the direction of the motion.
Question 11: Why is a coil of wire used in a generator instead of just a single straight wire?
Answer: Using a coil means that each turn of the wire cuts the magnetic field lines, so the induced potential difference from each turn adds up, producing a much larger overall voltage.
Question 12: If a coil has 100 turns, how many times is the magnetic field being cut when the magnet passes through it?
Answer: The field lines are effectively cut 100 times for each pass.
Question 13: A teacher drops a magnet from above a coil. As it enters the coil, a current is induced. What happens to the current as the magnet falls completely through the coil and comes out the other side?
Answer: The current will stop as the magnet passes through the centre of the coil (where it is not moving relative to the field), and then a current will be induced in the opposite direction as it leaves the coil.
Answer Walkthrough: The motion is reversed as the magnet exits the coil, so the direction of the induced current also reverses.
Question 14: What is the general name for the process of using a magnetic field and motion to produce electricity?
Answer: Electromagnetic Induction.
Question 15: What real-world device uses this principle to convert the kinetic energy of rotation into electrical energy?
Answer: A generator or dynamo.