Q1
What is the SI unit of electric current?
- (1)Volt
- (2)Ohm
- (3)Ampere✓ Correct answer
- (4)Watt
Answer: (3) Ampere
Explanation
The ampere (A) is the SI base unit of electric current.
Physics MCQ with Answers
20 questionswith explanationsfor RAS, Patwari, VDO and other Rajasthan exams
Questions
Q2
What is the SI unit of force?
- (1)Newton✓ Correct answer
- (2)Joule
- (3)Watt
- (4)Pascal
Answer: (1) Newton
Explanation
The SI unit of force is the newton (N); 1 N = 1 kg·m/s².
Q3
What is the approximate speed of light in vacuum?
- (1)3 × 10⁶ m/s
- (2)3 × 10⁵ m/s
- (3)3 × 10⁸ m/s✓ Correct answer
- (4)3 × 10¹⁰ m/s
Answer: (3) 3 × 10⁸ m/s
Explanation
Light travels in vacuum at about 3 × 10⁸ m/s (about 3 lakh km per second).
Q4
Which lens is used to correct myopia (short-sightedness)?
- (1)Convex lens
- (2)Concave lens✓ Correct answer
- (3)Cylindrical lens
- (4)Bifocal lens
Answer: (2) Concave lens
Explanation
In myopia the image forms in front of the retina; a concave (diverging) lens corrects it.
Q5
What is the SI unit of electrical resistance?
- (1)Ampere
- (2)Volt
- (3)Coulomb
- (4)Ohm✓ Correct answer
Answer: (4) Ohm
Explanation
Electrical resistance is measured in ohm (Ω).
Q6
Sound cannot travel through which of the following?
- (1)Vacuum✓ Correct answer
- (2)Water
- (3)Steel
- (4)Air
Answer: (1) Vacuum
Explanation
Sound is a mechanical wave and needs a material medium, so it cannot travel through vacuum.
Q7
The blue colour of the clear sky is due to which phenomenon?
- (1)Reflection of light
- (2)Total internal reflection
- (3)Scattering of light✓ Correct answer
- (4)Interference of light
Answer: (3) Scattering of light
Explanation
Air molecules scatter shorter (blue) wavelengths much more than longer ones, making the sky look blue.
Q8
What is the power of a convex lens of focal length 0.5 m?
- (1)+0.5 D
- (2)+2 D✓ Correct answer
- (3)−2 D
- (4)+5 D
Answer: (2) +2 D
Explanation
Power P = 1/f (in metres) = 1/0.5 = +2 dioptre; a convex lens has positive power.
Q9
A potential difference of 12 V is applied across a 4 Ω resistor. What current flows through it?
- (1)48 A
- (2)0.33 A
- (3)16 A
- (4)3 A✓ Correct answer
Answer: (4) 3 A
Explanation
By Ohm's law, I = V/R = 12/4 = 3 A.
Q10
Kilowatt-hour (kWh) is a unit of which quantity?
- (1)Energy✓ Correct answer
- (2)Power
- (3)Electric current
- (4)Electric charge
Answer: (1) Energy
Explanation
kWh is the commercial unit of electrical energy; 1 kWh = 3.6 × 10⁶ J.
Q11
What is the approximate value of acceleration due to gravity (g) on the Earth's surface?
- (1)6.8 m/s²
- (2)1.6 m/s²
- (3)9.8 m/s²✓ Correct answer
- (4)98 m/s²
Answer: (3) 9.8 m/s²
Explanation
The value of g near the Earth's surface is about 9.8 m/s²; on the Moon it is about 1.6 m/s².
Q12
What is the audible frequency range for a normal human ear?
- (1)2 Hz to 2,000 Hz
- (2)20 Hz to 20,000 Hz✓ Correct answer
- (3)200 Hz to 200,000 Hz
- (4)20,000 Hz to 2,00,000 Hz
Answer: (2) 20 Hz to 20,000 Hz
Explanation
Humans can hear sounds from about 20 Hz to 20 kHz; below is infrasound and above is ultrasound.
Q13
Optical fibres work on which principle?
- (1)Total internal reflection✓ Correct answer
- (2)Dispersion of light
- (3)Diffraction of light
- (4)Polarisation of light
Answer: (1) Total internal reflection
Explanation
Light is guided through an optical fibre by repeated total internal reflection at the core–cladding boundary.
Q14
A car starts from rest and accelerates uniformly to a velocity of 20 m/s in 5 s. What distance does it cover in this time?
- (1)100 m
- (2)25 m
- (3)50 m✓ Correct answer
- (4)40 m
Answer: (3) 50 m
Explanation
Acceleration a = 20/5 = 4 m/s², so s = ½at² = ½ × 4 × 5² = 50 m.
Q15
A force of 10 N moves a body through 5 m, the force acting at an angle of 60° to the direction of displacement. What is the work done by the force?
- (1)50 J
- (2)43.3 J
- (3)12.5 J
- (4)25 J✓ Correct answer
Answer: (4) 25 J
Explanation
W = Fs cos θ = 10 × 5 × cos 60° = 10 × 5 × 0.5 = 25 J.
Q16
If the velocity of a moving body is doubled while its mass stays the same, its kinetic energy becomes:
- (1)Two times
- (2)Half
- (3)Four times✓ Correct answer
- (4)Eight times
Answer: (3) Four times
Explanation
Kinetic energy = ½mv², so it varies as the square of velocity; doubling v makes KE 2² = 4 times.
Q17
Consider the following statements: 1. The mass of a body on the Moon is the same as its mass on the Earth. 2. The value of acceleration due to gravity (g) on the Earth's surface is maximum at the equator. Which of the statements given above is/are correct?
- (1)1 only✓ Correct answer
- (2)2 only
- (3)Both 1 and 2
- (4)Neither 1 nor 2
Answer: (1) 1 only
Explanation
Mass is constant everywhere, but g is maximum at the poles and minimum at the equator because the Earth's equatorial radius is larger.
Q18
Arrange the following electromagnetic radiations in increasing order of wavelength: 1. Microwaves 2. X-rays 3. Visible light 4. Radio waves
- (1)3, 2, 1, 4
- (2)2, 3, 1, 4✓ Correct answer
- (3)2, 3, 4, 1
- (4)4, 1, 3, 2
Answer: (2) 2, 3, 1, 4
Explanation
Wavelength increases in the order X-rays < visible light < microwaves < radio waves.
Q19
When a moving bus stops suddenly, the standing passengers tend to fall forward. This is due to:
- (1)Inertia of rest
- (2)Inertia of direction
- (3)Conservation of energy
- (4)Inertia of motion✓ Correct answer
Answer: (4) Inertia of motion
Explanation
The passengers' bodies tend to continue moving forward when the bus stops; this is inertia of motion (Newton's first law).
Q20
In which of the following media does sound travel the fastest?
- (1)Water
- (2)Air
- (3)Steel✓ Correct answer
- (4)Hydrogen gas
Answer: (3) Steel
Explanation
Sound travels fastest in solids; its speed in steel (about 5,960 m/s) is far higher than in water, hydrogen or air.