Showing 11–20 of 106 questions
in Physics
A lens has a focal length of 15 cm. What is its power?
A
+6.67 D
B
-6.67 D
C
+2.25 D
D
-2.25 D
Correct Answer:
A. +6.67 D
Explanation:
Power P = 1/f (in meters). P = 1/0.15 = 6.67 Diopters (positive for converging lens)
An object is placed 30 cm in front of a concave mirror with focal length 10 cm. Where is the image formed?
A
15 cm behind the mirror
B
15 cm in front of the mirror
C
20 cm in front of the mirror
D
20 cm behind the mirror
Correct Answer:
A. 15 cm behind the mirror
Explanation:
Using mirror formula 1/f = 1/u + 1/v, where f = -10 cm, u = -30 cm, we get v = -15 cm (behind mirror)
Which phenomenon explains the formation of a rainbow?
A
Refraction and dispersion
B
Reflection only
C
Diffraction only
D
Interference only
Correct Answer:
A. Refraction and dispersion
Explanation:
Rainbows form due to refraction of sunlight entering water droplets and dispersion of different wavelengths
A transformer has 500 turns in primary and 100 turns in secondary coil. If primary voltage is 220V, what is the secondary voltage?
A
44 V
B
1100 V
C
22 V
D
110 V
Explanation:
Using transformer equation Vs/Vp = Ns/Np, we get Vs = 220 × (100/500) = 44 V
What is the angle of incidence when light ray falls on a plane mirror and the angle of reflection is 35°?
Explanation:
According to law of reflection, angle of incidence equals angle of reflection
A current-carrying conductor is placed in a magnetic field perpendicular to it. What force acts on it?
A
Gravitational force
B
Lorentz force
C
Electrostatic force
D
Frictional force
Correct Answer:
B. Lorentz force
Explanation:
The force on a current-carrying conductor in a magnetic field is called the Lorentz force, given by F = BIL
Which of the following has the lowest refractive index?
A
Water
B
Glass
C
Air
D
Diamond
Explanation:
Air has a refractive index of approximately 1, which is the lowest among common materials
A radioactive element has a half-life of 10 years. After 30 years, what fraction of the original sample remains?
Explanation:
After 3 half-lives (30 years), the fraction remaining = (1/2)³ = 1/8
Which statement about elastic collisions is correct?
A
Momentum is not conserved
B
Kinetic energy is conserved
C
Objects always stick together
D
Maximum energy is lost
Correct Answer:
B. Kinetic energy is conserved
Explanation:
In elastic collisions, both momentum and kinetic energy are conserved
What is the young's modulus of a material?
A
Stress/Strain
B
Strain/Stress
C
Force × Area
D
Force/Volume
Correct Answer:
A. Stress/Strain
Explanation:
Young's modulus Y = Stress/Strain = (F/A)/(ΔL/L), a measure of material stiffness
