Question

Question 3, chap 131, sect 1. part 1 of 1 10 points Question 9, chap 131, sect 4 part 3 of 3 10 points What is the direction of the current flow A two-turn circular wire loop of radius through the loop containing the moving bar 0.628 m lies in a plane perpendicular to a and the resistor before (while the bar is on the uniform magnetic field of magnitude 0.325 T.right side of resistor) and after (while the bar Now the wire is reshaped from a two-turnon the left side of resistor) the bar passes the circle to a one-turn circle in 0.0419 s (while resistor? remaining in the sane plane) What is the magnitude of the average in-1, before (right-side): I is directed upward duoed emf in the wire during this time? Answer in units of V in the 9 Stresi star and after (ieft-side): In is directed upward in the 9 Ω resistor Question 4, chap 131, sect 1 part 1 of 1 10 points 2. before (right-side): In is directed upward in the 9t resistor and A magnetic field of 0.138 T exists in the re after (left-side: I0. gion enclosed by a solenoid that has 714 turns and a diameter of 4.95 cm. 3. before (right-side): I, is directed down- ward in the 9 Ω resistor and Within what period of time must the field be reduced to zero if the average magnitude ofthe induced etnf within the coil during this time interval is to be 5.82 kV Answer in units of s after (left-side): I is directed upward in the 9 Ω resistor. 4. before (right-side): In is directed upward nte 9 Ω resistor and Question 7, chap 131, sect 4. part 1 of 3 10 points after (left side): I is directed downward ir the n resstet In the arrangement shown in the figure, the resistor is 9 Ω and a 3 T magnetic field is directed into the paper. Assume the bar and rails have negligible resistance and frle- tion. The separation between the rails is 7 m 5. before (right-side): Ia is directed down ward in the 9 Ω resistor and 6. before (right-side): Is is directed down- ward in the 9 8 resistor and Neglect the mass of the bar. An applied force moves the bar to the left after (left-side): I, is directed downward in the g Ω resistor at a constant speed of 6 m/s 7, before (right-side): 4-0 and after (left-side): I0 Question 12, chap 131, sect 3. part 1 of 1 10 points 3 T Up down Consider a loop of wire with a resistor. In the same plane, (with switch S closed) a long wire has a current I flowing from left to right. What is the magnitude of the current in the resistor? Answer in units of A. Question 8, chap 131, sect 4. part 2 of 3 10 points What is the magnitude of the horizontal If switch S is closed for a long period of force F required to keep the bar moving at time, and then suddenly opened, what is the constant speed? Answer in units of N the current I rapidly decreases? 1. There is no current flow. 2. The current flows right to left through R. 3. The current flows left to right through R.

Questions 3,4,7,9,12...and thanks for the help...

Answer 1

3. Area of the loop, A = $\pi$ r^2 = [3.14*(0.628)^2]m^2 = 1.24 m^2

Flux linked with the coil with 2 number of turns $\phi$ 1 = NBA = 2BA

& flux linked with one turn, $\phi$ 2 = NBA = BA

So, induced emf, e = -(change in flux)/time interval

Or, e = -( $\phi$ 2 - $\phi$ 1)/t = 2BA - BA/t = BA/t = (0.325*1.24/0.0419) V

=   9.62 V

7. Motional emf induced in the bar, e = BLv , where 'B' is the magnetic field, 'v' is the velocity of the bar and 'L' is the length of the bar.

So, e = (3*7*6) = 126 volt  

Hence, magnitude of current in the resistor is given by, I = e/R = (126/9) = 14 ampere

8. External force required, F = ILB = (14*7*3) N =   294 N

12. When the switch is closed for long time, the left to right flowing current produces a magnetic field in the location of the loop, which, by right hand thumb rule, acts perpendicular to the plane of the loop and coming out of the plane. When switch is suddenly opened current in the wire and hence the magnetic field decreases from maximum to zero. So, according to Lenz's law, the induced current through the resistor will flow from right to left so as to give an induced magnetic field coming out of the plane of the loop to support the decreasing field. Option 2.