Question

1.

When a metal bar is pushed to the right in a metallic rectangular rail a current flows as shown in the figure. The rail is on a magnetic field that is not shown. The magnetic field must point? Up along the metal bar.Down along the metal bar.Out of the screen.Into the screen. 2. The diagram show the direction of magnetic field generated inside a solenoid due to the flow of current. What is the direction of the current in this solenoid, as viewed from the right side of the sketch? In the opposite to magnetic field. Counter clockwise. In the direction magnetic field. Clockwise.

3.

1. (10)   What is the magnitude and direction of magnetic field at point P due to the current in the loop?

   4.7 x 10-3 T out of page.

   4.7 x 10-5 T out of page.

   4.7 x 10-3 T into the page.

   4.7 x 10-5 T into the page.

4.

A 40 mA current is generated in an experiment by sliding a conducting rod at 4.0 m/s on metal rails separated by 2.0 m. What is the value magnetic field indicated by x in the sketch? Assume R is 0.36 Ω. 0.028 T 0.11 T 14 mT 3.6 mT 1.8 mT

5. A transformer has 400 turns on its primary and 18 turns on its secondary. If the power input to the ideal transformer is 120 kW, what is the power output at the secondary? 0.600 kW 7.20 kW 10.0 kW 120 kW During a demonstration in our classroom, I hold a big magnet right under the big table pointing north pole up. When I lower the magnet the magnetic field strength decreases from a value of 0.728 T to 0.150 T uniformly in 0.238 s. If a metal loop with an area of 0.450 m2  is laying flat on the table during the demonstration, what is the induced emf in the loop? 2.4 V 0.26 V zero 1.7 V 1.1 V W

7.You are trying to increase the induced emf using a loop and a source of magnetic field such as magnet. Which of the following changes would help to achieve your goal? Reducing the diameter of the loop. Turning the plane of the loop to be parallel to the magnetic field. Changing the magnetic field more rapidly. Reducing the resistance of the wire of which the loop is made

8.A bar magnet sits inside a coil of wire that is connected to a meter. The bar magnet is pulled out of the coil. What can we say about the current in the meter? There is no enough information to answer this question. The current goes from right to left. The current goes from left to right. There is no current in the meter.

What is true about the induced current in the rectangular loop?

	There is a counterclockwise induced current in the loop.
	There is a clockwise induced current in the loop.
	There is no induced current in the loop.
	Direct current in the wire can't induce current in the loop.

Answer 1

1)

from lenz law = emf = -(d/dt)(flux)

the current flows to oppose the change in flux

as the bar moves right the flux decreases.

the magnetic field is pointing into the screen

++

2)

from thr right curl rule

the current is in counterclock wise direction

++++++++++++

4) i = e/R = B*vl/R

B = iR/vl

B = (40*10^-3*0.36)/(4*2) = 1.8 mT

5)

for transformer Pout = Pin = 120 kW