Problem 1: A circular coil enclosing an area of 110 cm ^2 is made of 195 turns o
ID: 1521763 • Letter: P
Question
Problem 1:
A circular coil enclosing an area of 110 cm ^2 is made of 195 turns of copper wire (shown in the figure.) The write making up the coil has no resistance, the ends of the wire are connected across 2.00 resistor to form a closed circuit. Initally a 1.50 T uniform magnetic field ponts perpendicularly upward throught h eplane of the coil. the direction of the field then reverses to that the final magnetic filed has a magnitude of 1.50 T and points downward through the coil. if the time interval required fo the field to reverse directions is 0.350s, what is the average current in the coil during that time?
Problem 2.
A concave mirror wiht a 40 cm radius of curvature is placed 10 cm in front of a 10 cm tall candle.
a. find the location and size of the image.
b. suppose you want to replace the mirror in part a wiht a lens (n =1.4) and still get the same image ( in size and position ) for the same object. design such a lens (determine the radius of curvature of its two surfaces ) note that there ar emany correct ansewrs to this question.
Explanation / Answer
Flux change = A*dB = 0.011*3 = 0.033
EMF = n*flux change/time = 18.3857 V
I = V/R = 9.19285 A
h = 10 cm
u = -10 cm
f = -20 cm
1/v + 1/u = 1/f
v = 20 cm
to make a lens, we use
1/v - 1/u = 1/f
f = 6.6667 cm
1/f = (n-1)(1/R + 1/R) (lens makers formula)
R = 5.333 cm