Light and Optics Practice Questions
Thanaweya Amma (Egypt) · Thanaweya Physics · 136 free MCQs with instant results and detailed explanations.
136
Total
40
Easy
75
Medium
21
Hard
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Sample Questions from Light and Optics
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Q1
Easy
What happens to light when it passes from air into water?
A.
It speeds up.
B.
It changes direction.
C.
It reflects off the surface.
D.
It disappears.
Show Answer & Explanation
Correct Answer: B
Light bends when it enters a medium with a different density, which causes a change in direction. This phenomenon is called refraction.
Q2
Easy
If the focal length of a concave lens is -15 cm, what is the power of the lens?
A.
-6.67 D
B.
6.67 D
C.
-15 D
D.
15 D
Show Answer & Explanation
Correct Answer: A
The power (P) of a lens is calculated using the formula P = 1/f (in meters). For a focal length of -15 cm (or -0.15 m), P = 1/(-0.15) = -6.67 D.
Q3
Easy
What is the speed of light in a vacuum?
A.
3 x 10^8 m/s
B.
1.5 x 10^8 m/s
C.
3 x 10^10 m/s
D.
1 x 10^9 m/s
Show Answer & Explanation
Correct Answer: A
The speed of light in a vacuum is approximately 3 x 10^8 meters per second, which is a fundamental constant of nature.
Q4
Medium
What is the refractive index of a material if the speed of light in vacuum is 3 x 10^8 m/s and the speed of light in the material is 2 x 10^8 m/s?
A.
1.5
B.
0.67
C.
1.2
D.
2.0
Show Answer & Explanation
Correct Answer: A
The refractive index is calculated as the ratio of the speed of light in vacuum to the speed of light in the material. Thus, n = c/v = (3 x 10^8)/(2 x 10^8) = 1.5.
Q5
Medium
A beam of light passes from air into water at an angle of incidence of 30 degrees. What is the angle of refraction in the water? (Refractive index of water = 1.33)
A.
22.0 degrees
B.
30.0 degrees
C.
23.0 degrees
D.
45.0 degrees
Show Answer & Explanation
Correct Answer: A
Using Snell's Law, n1 * sin(ฮธ1) = n2 * sin(ฮธ2), with n1 for air being 1, we find sin(ฮธ2) = sin(30) / 1.33. Solving gives ฮธ2 โ 22.0 degrees.
Q6
Medium
A light ray strikes a mirror at an angle of 45 degrees. What will be the angle of reflection?
A.
0 degrees
B.
45 degrees
C.
90 degrees
D.
135 degrees
Show Answer & Explanation
Correct Answer: B
According to the law of reflection, the angle of incidence is equal to the angle of reflection. Thus, if the angle of incidence is 45 degrees, the angle of reflection is also 45 degrees.
Q7
Medium
What is the critical angle for total internal reflection when light travels from glass (n=1.5) to air (n=1.0)?
A.
41.8 degrees
B.
45.0 degrees
C.
60.0 degrees
D.
30.0 degrees
Show Answer & Explanation
Correct Answer: A
The critical angle (ฮธc) can be found using the formula ฮธc = sin^(-1)(n2/n1). Here, ฮธc = sin^(-1)(1.0/1.5) โ 41.8 degrees.
Q8
Hard
A convex lens has a focal length of 10 cm. An object is placed 15 cm from the lens. What is the position of the image formed by the lens?
A.
30 cm on the opposite side
B.
7.5 cm on the same side
C.
20 cm on the opposite side
D.
5 cm on the same side
Show Answer & Explanation
Correct Answer: C
Using the lens formula 1/f = 1/v - 1/u, where f = 10 cm (focal length), u = -15 cm (object distance). Rearranging gives us v = 1/(1/f + 1/u). Plugging in the values leads to the image distance v = 20 cm on the opposite side of the lens.
Q9
Hard
A concave mirror has a focal length of 20 cm. An object is placed 60 cm in front of the mirror. What is the distance of the image from the mirror?
A.
15 cm
B.
30 cm
C.
45 cm
D.
50 cm
Show Answer & Explanation
Correct Answer: C
Using the mirror formula (1/f = 1/v + 1/u), where f is the focal length (20 cm), u is -60 cm (object distance is negative for mirrors), we find v = 45 cm, which means the image is 45 cm from the mirror.
Q10
Hard
When white light passes through a prism, which color deviates the least and why?
A.
Red, because it has the longest wavelength
B.
Blue, because it has the shortest wavelength
C.
Green, because it is in the middle of the spectrum
D.
Violet, because it is least refracted
Show Answer & Explanation
Correct Answer: A
Red light has the longest wavelength among the visible spectrum, which results in the least amount of refraction when passing through a prism, thus deviating the least.
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Light and Optics โ Thanaweya Amma (Egypt) Thanaweya Physics Practice Questions Online
This page contains 136 practice MCQs for the chapter Light and Optics in Thanaweya Amma (Egypt) Thanaweya Physics. The questions are organized by difficulty โ 40 easy, 75 medium, 21 hard โ so you can choose the right level for your preparation.
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