Q: A 1.5 W lightbulb is placed 50 cm below a plane mirror. A sensor is placed 70 cm horizontally from the bulb, with a barrier blocking direct light. What is the intensity at the sensor due to the reflected light? Use $$I = \frac{P}{4\pi r^2$}$$ and the path length $$r = 1.22 m.$$

$$8.0 \times 10$$^{-2}$$~\mathrm{W/m^2$}$$

Question 1

A point object O is placed in front of a plane mirror as shown in the diagram. From which locations (A, B, C, D) is the image of O visible in the mirror, according to the law of reflection?

Accepted Answer

Only from locations B and C

Question 2

A 1.5 W lightbulb is placed 50 cm below a plane mirror. A sensor is placed 70 cm horizontally from the bulb, with a barrier blocking direct light. What is the intensity at the sensor due to the reflected light? Use $$I = \frac{P}{4\pi r^2$}$$ and the path length $$r = 1.22 m.$$

Accepted Answer

$$8.0 	imes 10$$^{-2}$$~\mathrm{W/m^2$}$$

Question 3

A light ray in air strikes a 1.0-cm-thick layer of water at $$60^\circ$$ from the normal. After passing through the water and entering glass, what is the angle from the normal in the glass? ($$n_{	ext{air}} = 1.0$$, $$n_{	ext{water}} = 1.33$$, $$n_{	ext{glass}} = 1.50)$$

Accepted Answer

$$35^\circ$$

Question 4

A ray of light enters an equilateral prism at $$	heta = 40^\circ$$ from the normal and emerges at the same angle. If the prism is equilateral, what is the index of refraction of the prism? (Use Snell's law: $$n_{	ext{air}} \sin 	heta_{	ext{air}} = n_{	ext{prism}} \sin 	heta_{	ext{prism}})$$

Accepted Answer

$$1.5$$

Question 5

A thin glass rod ($$n_{	ext{glass}} = 1.50) is $$submerged in oil ($$n_{	ext{oil}} = 1.46). $$What is the critical angle for light traveling inside the rod? (Use $$\sin 	heta_c = \frac{n_{	ext{oil}}}{n_{	ext{glass}}})$$

Accepted Answer

$$76.7^\circ$$

Question 6

A light ray travels inside a block of sodium fluoride ($$n = 1.33) $$and strikes the vertical wall at the critical angle, totally reflects, and then emerges into air ($$n = 1.00). $$What is the angle $$\$$theta_2$$ at which the ray emerges into air? (Use Snell's law and $$\sin 	heta_c = \frac{n_{	ext{air}}}{n_{	ext{NaF}}}$$)

Accepted Answer

$$61.3^\circ$$

Question 7

Which of the following best describes the law of reflection for a ray striking a plane mirror?

Accepted Answer

The angle of incidence equals the angle of reflection

Question 8

If the index of refraction of a material increases, what happens to the speed of light in that material?

Accepted Answer

The speed of light decreases

Question 9

A light ray passes from water ($$n=1.33) $$into glass ($$n=1.50). If $$the incident angle in water is $$40^\circ$$, what is the angle of refraction in glass? (Use Snell's law)

Accepted Answer

$$34.6^\circ$$

Question 10

Which of the following is a necessary condition for total internal reflection to occur?

Accepted Answer

Light must travel from a medium with higher index of refraction to one with lower index

Question 11

A ray of light in air strikes a glass surface ($$n=1.50) at$$ $$30^\circ$$ from the normal. What is the angle of refraction inside the glass? (Use Snell's law)

Accepted Answer

$$19.5^\circ$$

Question 12

If a light ray passes from air into water at $$60^\circ$$ from the normal, what is the angle of refraction in water? ($$n_{	ext{air}} = 1.0$$, $$n_{	ext{water}} = 1.33)$$

Accepted Answer

$$40.6^\circ$$

Question 13

A prism is made of glass with $$n=1.5. If a $$light ray enters at $$50^\circ$$ from the normal, what is the angle of refraction inside the prism? (Use Snell's law)

Accepted Answer

$$30^\circ$$

Question 14

A light ray in glass ($$n=1.50) is $$incident at the glass-oil interface. If the critical angle is $$76.7^\circ$$, what is the index of refraction of the oil?

Accepted Answer

$$1.46$$

Question 15

A light ray in sodium fluoride ($$n=1.33) $$strikes the interface with air at the critical angle. What is the value of the critical angle?

Accepted Answer

$$48.75^\circ$$

Question 16

Which of the following best explains why the image of an object in a plane mirror appears to be the same distance behind the mirror as the object is in front?

Accepted Answer

The law of reflection causes all reflected rays to appear to originate from a point behind the mirror

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