Question

1. There was a noticeable time delay in the radio communications between NASA and theApollo team on the surface of the moon. The distance between the Earth and Moon isapproximately 384,400km. How long does it take an electromagnetic signal to reach theEarth from this distance? (Note: c=2.99792x10⁸ m/s)

		4.277 ns
		1.282 ms
		1.282 s
		26.18 s

4. A light source has a wavelength of 632 nm in a vacuum. Calculate the frequency of the light source as measured within a material with an index of refractionn= 4/3.

		4.74×105Hz
		3.56×105Hz
		4.74×1014Hz
		6.32×105Hz
		3.56×1014Hz

5. The world’s most powerful laser (circa 1998) was 1.3PW = 1.3×10¹⁵W. If the laser generated a 5cm radius beam, calculate the strength of the MAGNETIC field in thebeam.

		37.24T
		10.2×1013T
		1.12×1010T
		1.25×1020T

6. You are using a green laser pointer (presumably water proof) to shine light out of a fishtank. What is the maximum angle the light can make, with respect to the normal, as the light passes from water (n= 1.3333) to glass (n= 1.5)?

		46°
		42°
		63°
		There is no maximum angle

14. A transformer is powered by applying 1V amplitude AC signal across a primary wound with 10wraps. The secondary is wound with 100wraps. What voltage will be measured across the secondary?

		0.1 V
		1 V
		10 V
		100 V

15. A time dependent electric field, E(t)=100t²-5/t N/C, is measured across a parallel plate capacitor of radius r = 15cm. What is the displacement current at time t =2s?

		0A
		2.5x10-10 A
		1.68x10-9
		3.55x10-9 A

Answer 1

1. from speed = distance travelled / time taken

time taken = distance / speed

= 384,400 km / (2.99792 x 10⁸ m/s)

= 384,400 x 10³ / ( 2.99792 x 10⁸ m/s)

= 128222 x 10^-5

= 1.281 second

2. frequency of light in vacuum = speed of light in vacuum / wavelength

= 2.99792 x 10⁸ ms^-1/ (632 x 10^-9 m)

= 0.004744 x 10¹⁷

= 4.744 x 10¹⁴ Hz = frequency of light in the given material

frequency of light reamins unaltered when light travels from one medium to other.

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