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 Electromagnetic Induction Physlet® Problems

#### Physlets® used by permission of Wolfgang Christian, Davidson College. Physlet® Problems ©Prentice Hall, Inc. Physlet® problems on this web site were written by Wolfgang Christian, Mario Belloni, and Aaron Titus.

1 .

The animation shows a top view of four wires and a galvanometer in the lab.  Current flowing into the + terminal, i.e., counterclockwise, will deflect the meter to the right.   During the time interval t=2 s to t=8 s a magnet is slowly pushed completely through  the rectangle from the bottom toward the top. (You can also think of  the magnet as being pushed out of the computer monitor toward the user.) Observe the meter reading during this simulation.  Which pole was inserted first? North or south? The animation starts at t=0 and stops at t=10 seconds.    Start.

[Hint]

 North. South.

2 .

The animation shows a top view of four wires and a galvanometer.  There is a constant magnetic field passing through these wires.  Determine the direction of this magnetic field by click-dragging the black wire back and forth and observing the galvanometer reading.  Remember that current flowing into the + terminal, i.e., counterclockwise, will deflect the meter to the right.   Start.

[Hint]

 Toward the top.  That is, out of the computer monitor. Toward the bottom.  That is, into the computer monitor.

3 .

A loop of wire sits in a time varying magnetic field (a positive magnetic field is out of the screen). You may drag the loop around the animation. Given the flux calculation given above, what is the magnitude and direction of the emf induced in the wire during the animation?    Start.

[Hint]

 3.9 V counterclockwise. Insufficient Information. 39 V clockwise. 3.9 V clockwise.

4 .

A loop of wire travels from the right to the left through an inhomogeneous magnetic field. (The green line is at x=0 is for your reference.) The induced emf in the loop is shown in Volts in the animation. Describe the magnetic field perpendicular to the computer screen.   Start.

[Hint]

 Bz(x<0)=0, Bz(x>0)>0. Bz(x<0)=constant, Bz(x>0)=constant, and Bz(x<0)< Bz(x>0). Bz(x<0)=constant, Bz(x>0)=constant, and Bz(x<0)> Bz(x>0). Bz(x<0)<0, Bz(x>0)=0. Bz is uniform.

5 .

The wire on the right is pulled to the right for 5 seconds and then to the left for 5 seconds as shown.  Determine the magnitude of the magnetic field passing through the wire rectangle.  You may pause the simulation and read coordinate values by click-dragging the mouse at any time. The meter displays the induced emf in millivolts.  Start.

More Help Plot the input and output voltage as functions of time. See Section 20.1 in Wilson and Buffa.

[Hint]

 1 milli-Tesla. 2 milli-Tesla. 3 milli-Tesla. 4 milli-Tesla.

6 .

A loop of wire moves to the right through a magnetic field (a positive magnetic field is out of the screen) that abruptly goes to zero at x=0. Given the flux calculation given above, what is the magnitude and direction of the emf the the wire undergoes the field transition at x=0?   Start.

[Hint]

 19.2 V counterclockwise. Insufficient Information. 19.2 V clockwise. 0 V.

7 .

A loop of wire is to the right of a wire that runs up the computer screen (a positive magnetic field is out of the screen). In which direction is the current flowing in the wire?  Start.

[Hint]

 +y direction. Insufficient Information. -y direction.

8 .

The above animation represents a moving wire loop in a changing magnetic field (red indicates a field out of the screen and blue indicates a field into the screen). Which animation correctly represents both the voltage and flux through the loop as a function of time?

[Hint]

 Animation 1. Animation 2. Animation 3. Animation 4.

9 .

A transformer is connected to a wall socket as shown above. The graph shows the primary voltage Vp (black) and the secondary voltage Vs (red). How many turns Ns does the secondary coil carry when the primary coil carries Np = 200 turns? Start.

[Hint]

 1006. Insufficient Information. 200. 40.

10 .

A transformer is connected to a wall socket as shown above. The graph shows the primary voltage Vp (black) and the primary current Ip (red). Assume no heat loss in the transformer. Determine the electrical power send into the transformer. Start.

[Hint]

 42.5 kW. Insufficient Information. 30.5 kW. 5.5 MW.

11 .

A transformer is connected to a wall socket as shown.  How many turns are there in the transformer secondary if the transformer primary has 300 turns?   You can read component values by placing the mouse over a component.  Start.

### Interactive Hint

More Help. Plot the input and output voltage as functions of time.

[Hint]

 50 turns. 70 turns. 300 turns. 1800 turns.

12 .

A load is connected to a transformer as shown.  What how much rms current flows from the wall plug?  You can read component values by placing the mouse over a component.  Start.

More Help.

[Hint]

 0.2 A. 2 A. 20 A.

13 .

An electron, denoted by the red circle (position is in meters and time is in seconds), is shown in 4 animations. In which animations can the electron produce radiation?

[Hint]

 Animation 1. Animations 2 and 3. Animations 2, 3, and 4. All 4 animations.

14 .

The animation shows how static electric field lines from a positive point charge produce a radiation field if the charge is caused to oscillate.  Notice how the electric field lines form waves that move away from the charge.  What is the direction of the magnetic field associated with the waves to the right of the charge?   Start

[Hint]

 The magnetic field will point in the same direction as the electric field. The magnetic field will point into the computer monitor. The magnetic field will rotate up and down as the charge moves up and down. The magnetic field will alternate pointing into and out of the computer monitor.

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