物理光的反射和折射 DSE、CE 選擇題（第 2 頁）

11.

A ray of light is traveling from glass to air as shown in the figure. Which of the following ratios is the refractive index of glass ?

Ray from glass to air making angle theta with the boundary in glass and angle phi with the boundary in air

12.

Which of following statements about total internal reflection is/are correct ?

(1)The angle of incidence is less than the critical angle.

(2)Both reflected and refracted rays appear.

(3)The ray is travelling from an optically denser medium to an optically less dense medium.

13.

Pencil lying on a grid in front of a vertical plane mirror, with the eye below

A pencil is placed in front of a vertical plane mirror as shown in the figure above. Which of the following shows the correct position of the image ?

Four grids A to D showing the pencil image in different positions

14.

Light ray in water incident on an air bubble with possible emergent rays W, X, Y and Z

A light ray is incident from water onto an air bubble as shown above. Which light ray best represents the emergent ray ?

15.

Figure (a) shows a light ray travelling from air into medium $X$ . The angle of incidence is $50^\circ$ and the angle of refraction is $r$ . Another light ray travelling from medium $X$ to air is shown in Figure (b). The angle of incidence is $35^\circ$ and the angle of refraction is also equal to $r$ . What is angle $r$ ?

$Figure (a): ray from air into medium X at 50 degrees, refraction angle r. Figure (b): ray from medium X to air at 35 degrees, refraction angle r$

16.

John wants to estimate the speed of a cloud in the following experiment. The cloud is moving horizontally at a height of $3000$ m above the ground. He looks at the image of the cloud in a mirror of $0.6$ m wide placed on the horizontal ground $1.5$ m below his eye level. He finds that the image of the cloud takes $20$ s to move across the mirror.

Cloud at 3000 m, observer 1.5 m above a 0.6 m wide mirror on the ground, and the image of the cloud (not drawn to scale)

What is the approximate speed of the cloud ?

17.

Which of the following surfaces produce diffuse reflection when parallel light rays fall on them ?

(1)a blackboard in the classroom

(2)a polished metal surface

(3)a page in this question book

18.

A light ray enters normally into a right-angled prism and is totally internally reflected at face $AB$ as shown below. Based on this optical phenomenon, which of the following is/are the possible value(s) for the refractive index of the material of the prism ?

(1)

1.35

(2)

1.45

(3)

1.55

Ray entering a right-angled prism normally and reflected at face AB with a 45 degree angle at A

19.

The diagram shows the image of a clock formed in a plane mirror. What is the time displayed by the clock at this instant ?

20.

Martha 2 m behind Eric, and Eric 1 m in front of a plane mirror

Eric stands $1$ m in front of a plane mirror. Martha stands $2$ m behind Eric as shown above. Find the distance between Eric and the image of Martha formed by the mirror.