Physics 3172 final Exam Jan. 29, 2018 1. A transformer has 500 turns of the prim
ID: 1574282 • Letter: P
Question
Physics 3172 final Exam Jan. 29, 2018 1. A transformer has 500 turns of the primary winding and 10 turns of the secondary winding, a) Determine the secondary voltage if the secondary circuit is open and the primary voltage is 120 V. b) Determine the current in the primary and secondary winding, given that the secondary winding is connected to a resistance load 15 ? 2. An AC generator supplies an rms voltage of 200 V at 50.0 Hz. It is connected in series with a 0.500 H inductor, a 4.50 F capacitor and a 200 resistor. (a) What is the impedance of the circuit? (b) What is the rms current through the resistor? (c) What is the peak voltage across the inductor? (d) What is the resonance frequency? 3. An electromagnetic wave from a wire antenna travels (from the reader) out of the plane of the paper, as shown in Fig. 1. At time t-0.0 s it strikes the paper at normal incidence Atpoint O and 0.0 s, the magnetic field vector has its maximum value, 5.010" T pointing in the negative y-direction. The frequency of this wave is 1.5x10 Hz. (a) What is the electric field E at time t 0.0 s? (Use the right-hand rule to determine the direction of E.) (b) What is the Poynting vector of the wave at time t-0.0 s? Determine the magnitude and direction. (c) What is the magnetic field B at point O at time 1 0x10 s? 4. An object is placed 15.0 cm in front of a convex mirror with a radius of curvature 50.0 cm. (a) Determine the location of the image. (b) What is the magnification of the object discussed above? (c) Draw the rays to determine the image location in (a). 5. A single bi-concave lens made of glass with n=1.75, has surfaces with radii of curvature In-15cm and Ir-15em. (a) What is the focal length? (b) If the object is at 10cm from the lens, where is the image? (c) Draw the rays to determine the image location in (b). 6. With two slits spaced 0.2mm apart, and a screen at a distance of 1 m, the third bright fringe is found to be displaced h-7.5mm from the central fringe. Show that the wavelength, , of the light used is 5 x 10" B (t=0) Fig. 1 (5-A,BeB,H+¼(n-1)(LL),n,sina-r½sine.dainfnl)Explanation / Answer
1. (A) for transformer,
Ns/ Np = Vs / Vp
10 / 500 = Vs ./ 120
Vs = 2.4 volt
(B) Is = Vs / R_load
= 2.4 / 15
= 0.16 A
(C) Ip Vp = Is Vs
Ip (120) = (0.16) (2.4)
Ip = 3.2 x 10^-3 A or 3.2 mA