EM Induction Slides PDF

Electromagnetic Induction Really Useful Formulas: Φ𝐵 = 𝐵𝐴 cos 𝜃 ∆Φ𝐵 Δ(𝐵𝐴 cos 𝜃) ℇ = −𝑁 = −𝑁 Δ𝑡 Δ𝑡 ℇ=Blv Think about it Which of the following will cause an induced current in a coil of wire? A. A magnet...

Electromagnetic Induction Really Useful Formulas: Φ𝐵 = 𝐵𝐴 cos 𝜃 ∆Φ𝐵 Δ(𝐵𝐴 cos 𝜃) ℇ = −𝑁 = −𝑁 Δ𝑡 Δ𝑡 ℇ=Blv Think about it Which of the following will cause an induced current in a coil of wire? A. A magnet resting near the coil B. The constant field of the earth passing through the coil C. A magnet being moved into or out of the coil D. A wire carrying a constant current near the coil Think about it Which of the following will cause an induced current in a coil of wire? A. A magnet resting near the coil B. The constant field of the earth passing through the coil C. A magnet being moved into or out of the coil D. A wire carrying a constant current near the coil Think about it A metallic conductor moving at a constant speed in a magnetic field may develop a voltage across it. This is an example of Fill in th e blank. A. Faraday’s Law B. Lenz’s Law C. Motional emf D. Induced emf Think about it A metallic conductor moving at a constant speed in a magnetic field may develop a voltage across it. This is an example of Fill in the b lank. A. Faraday’s Law B. Lenz’s Law C. Motional emf D. Induced emf Think about it An emf is induced in response to a change in magnetic field inside a loop of wire. Which of the following changes would increase the magnitude of the induced emf? A. Reducing the diameter of the loop B. Turning the plane of the loop to be parallel to the magnetic field C. Changing the magnetic field more rapidly D. Reducing the resistance of the wire of which the loop is made Think about it An emf is induced in response to a change in magnetic field inside a loop of wire. Which of the following changes would increase the magnitude of the induced emf? A. Reducing the diameter of the loop B. Turning the plane of the loop to be parallel to the magnetic field C. Changing the magnetic field more rapidly D. Reducing the resistance of the wire of which the loop is made Think about it A metal bar moves through a magnetic field. The induced charges on the bar are Think about it A metal bar moves through a magnetic field. The induced charges on the bar are Think about it A metal bar moves through a magnetic field. The induced charges on the bar are Think about it A metal bar moves through a magnetic field. The induced charges on the bar are Think about it An induced current flows clockwise as the metal bar is pushed to the right. The magnetic field points A. Up. B. Down. C. Into the screen. D. Out of the screen. E. To the right. Think about it An induced current flows clockwise as the metal bar is pushed to the right. The magnetic field points A. Up. B. Down. C. Into the screen. D. Out of the screen. E. To the right. Think about it Which loop has the larger magnetic flux through it? A. Loop A B. Loop B C. The fluxes are the same. D. Not enough information to tell Think about it Which loop has the larger magnetic flux through it? A. Loop A B. Loop B  m = L2B C. The fluxes are the same. D. Not enough information to tell Think about it A loop of wire of area A is tipped at an angle θ to uniform magnetic field B. The maximum flux occurs for an angle θ = 0. What angle θ will give a flux that is 12 of this maximum value? A. θ = 30° B. θ = 45° C. θ = 60° D. θ = 90° Think about it A loop of wire of area A is tipped at an angle θ to uniform magnetic field B. The maximum flux occurs for an angle θ = 0. What angle θ will give a flux that is 12 of this maximum value? A. θ = 30° B. θ = 45° C. θ = 60° D. θ = 90° Think about it The metal loop is being pulled through a uniform magnetic field. Is the magnetic flux through the loop changing? A. Yes B. No Think about it The metal loop is being pulled through a uniform magnetic field. Is the magnetic flux through the loop changing? A. Yes B. No Think about it The metal loop is rotating in a uniform magnetic field. Is the magnetic flux through the loop changing? A. Yes B. No Think about it The metal loop is rotating in a uniform magnetic field. Is the magnetic flux through the loop changing? A. Yes B. No Try this At a particular location, the earth’s magnetic field is 50  T tipped at an angle of 60° below horizontal. A 10-cm-diameter circular loop of wire sits flat on a table. What is the magnetic flux through the loop? Try this (solution) FIND THE ANGLE AND AREA: The figure shows the loop and the field of the earth. The field is tipped by 60°, so the angle of the field with respect to the axis of the loop is θ = 30°. The radius of the loop is 5.0 cm, so the area of the loop is A =  r =  ( 0.050 m ) = 0.0079 m2. 2 2 Try this (solution) SOLVE: The flux through the loop is then ( )( )  = AB cos  = 0.0079m2 50  10 −6 T cos30° = 3.4  10 −7 Wb Really Useful Formulas: Φ𝐵 = 𝐵𝐴 cos 𝜃 ∆Φ𝐵 Δ(𝐵𝐴 cos 𝜃) ℇ = −𝑁 = −𝑁 Δ𝑡 Δ𝑡 ℇ=Blv Think about it The bar magnet is pushed toward the center of a wire loop. Which is true? A. There is a clockwise induced current in the loop. B. There is a counterclockwise induced current in the loop. C. There is no induced current in the loop. Think about it The bar magnet is pushed toward the center of a wire loop. Which is true? A. There is a clockwise induced current in the loop. B. There is a counterclockwise induced current in the loop. C. There is no induced current in the loop.  Think about it The bar magnet is pushed toward the center of a wire loop. Which is true? A. There is a clockwise induced current in the loop. B. There is a counterclockwise induced current in the loop. C. There is no induced current in the loop.  Think about it The bar magnet is pushed toward the center of a wire loop. Which is true? A. There is a clockwise induced current in the loop. B. There is a counterclockwise induced current in the loop. C. There is no induced current in the loop. Magnetic flux is zero, so there’s no change of flux.  Think about it A bar magnet sits inside a coil of wire that is connected to a meter. For each of the following circumstances 1. The bar magnet is at rest in the coil, 2. The bar magnet is pulled out of the coil, 3. The bar magnet is completely out of the coil and at rest, 4. The bar magnet is reinserted into the coil, What can we say about the current in the meter? A. The current goes from right to left. B. The current goes from left to right. C. There is no current in the meter.  Think about it A bar magnet sits inside a coil of wire that is connected to a meter. For each of the following circumstances 1. The bar magnet is at rest in the coil, C 2. The bar magnet is pulled out of the coil, A 3. The bar magnet is completely out of the coil and at rest, C 4. The bar magnet is reinserted into the coil, B What can we say about the current in the meter? A. The current goes from right to left. B. The current goes from left to right. C. There is no current in the meter. Think about it A magnetic field goes through a loop of wire, as at right. If the magnitude of the magnetic field is 1. Increasing, 2. Decreasing, 3. Constant, What can we say about the current in the loop? A. The loop has a clockwise current. B. The loop has a counterclockwise current. C. The loop has no current. Think about it A magnetic field goes through a loop of wire, as at right. If the magnitude of the magnetic field is 1. Increasing, B 2. Decreasing, A 3. Constant, C What can we say about the current in the loop? A. The loop has a clockwise current. B. The loop has a counterclockwise current. C. The loop has no current. Think about it The magnetic field is confined to the region inside the dashed lines; it is zero outside. The metal loop is being pulled out of the magnetic field. Which is true? A. There is a clockwise induced current in the loop. B. There is a counterclockwise induced current in the loop. C. There is no induced current in the loop. Think about it The magnetic field is confined to the region inside the dashed lines; it is zero outside. The metal loop is being pulled out of the magnetic field. Which is true? A. There is a clockwise induced current in the loop. B. There is a counterclockwise induced current in the loop. C. There is no induced current in the loop. Think about it A loop is moved toward a current-carrying wire as shown in the figure. As the wire is moving, is there a clockwise current around the loop, a counterclockwise current, or no current? Think about it A loop is moved toward a current-carrying wire as shown in the figure. As the wire is moving, is there a clockwise current around the loop, a counterclockwise current, or no current? Think about it A battery, a loop of wire, and a switch make a circuit as shown. A second loop of wire sits directly below. At the following times, 1. Just before the switch is closed, 2. Immediately after the switch is closed, 3. Long after the switch is closed, 4. Immediately after the switch is reopened, What can we say about the current in the lower loop? Answer for each of the stated conditions. A. The loop has a clockwise current. B. The loop has a counterclockwise current. C. The loop has no current. Think about it A battery, a loop of wire, and a switch make a circuit as shown. A second loop of wire sits directly below. At the following times, 1. Just before the switch is closed, C 2. Immediately after the switch is closed, A 3. Long after the switch is closed, C 4. Immediately after the switch is reopened, B What can we say about the current in the lower loop? Answer for each of the stated conditions. A. The loop has a clockwise current. B. The loop has a counterclockwise current. C. The loop has no current. Think about it Immediately after the switch is closed, the lower loop exerts fill in the blank on the upper loop. A. A torque B. An upward force C. A downward force D. No force or torque Think about it Immediately after the switch is closed, the lower loop exerts fill in the blank on the upper loop. A. A torque B. An upward force C. A downward force D. No force or torque Really Useful Formulas: Φ𝐵 = 𝐵𝐴 cos 𝜃 ∆Φ𝐵 Δ(𝐵𝐴 cos 𝜃) ℇ = −𝑁 = −𝑁 Δ𝑡 Δ𝑡 ℇ=Blv Try this The following figure shows a 10-cm-diameter loop in three different magnetic fields. The loop’s resistance is 0.1 Ω. For each situation, determine the magnitude and direction of the induced current. Transformers ∆Φ ∆Φ 𝑉𝑠 𝑁𝑠 𝑉𝑝 = 𝑁𝑝 𝑉𝑠 = 𝑁𝑠 = Δ𝑡 Δ𝑡 𝑉𝑝 𝑁𝑝 Summary: General Principles Electromagnetic Induction The magnetic flux measures the amount of magnetic field passing through a surface:  = AB cos  Summary: General Principles Electromagnetic Induction Lenz’s law specifies that there is an induced current in a closed conducting loop if the magnetic flux through the loop is changing. The direction of the induced current is such that the induced magnetic field opposes the change in flux. Summary: General Principles Electromagnetic Induction Faraday’s law specifies the magnitude of the induced emf in a closed loop:  =  t Multiply by N for an N-turn coil. The size of the induced current is I=  R Summary: General Principles Motional emf The motion of a conductor through a magnetic field produces a force on the charges. The separation of charges leads to an emf:  = vlB