Central Exam — General Science
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Showing 161–170 of 207 questions
Q.161 Medium Physics
A submarine sonar uses ultrasound with frequency 50 kHz and speed 1500 m/s in water. What is the wavelength?
A 0.03 m
B 0.3 m
C 3 m
D 30 m
Correct Answer:  A. 0.03 m
Explanation:

Wavelength λ = v/f = 1500/(50 × 10³) = 1500/50000 = 0.03 m = 3 cm. Higher frequencies in denser mediums produce shorter wavelengths.

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Q.162 Medium Physics
A conducting sphere is given a charge of 8 μC. What is the electric field at its surface if the radius is 2 cm?
A 1.8 × 10⁶ N/C
B 3.6 × 10⁷ N/C
C 1.8 × 10⁷ N/C
D 7.2 × 10⁷ N/C
Correct Answer:  C. 1.8 × 10⁷ N/C
Explanation:

Electric field at surface: E = kQ/r² = (9 × 10⁹ × 8 × 10⁻⁶)/(0.02)² = (72)/(4 × 10⁻⁴) = 1.8 × 10⁷ N/C.

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Q.163 Hard Physics
A Carnot engine operates between temperatures 400 K and 300 K. What is its maximum efficiency?
A 0.25 or 25%
B 0.33 or 33%
C 0.75 or 75%
D 0.50 or 50%
Correct Answer:  A. 0.25 or 25%
Explanation:

Carnot efficiency: η = 1 - (T_cold/T_hot) = 1 - (300/400) = 1 - 0.75 = 0.25 = 25%. This is the theoretical maximum for any heat engine.

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Q.164 Hard Physics
When light passes from a denser to a rarer medium at an angle greater than the critical angle, what happens?
A Light refracts away from normal
B Light undergoes total internal reflection
C Light partially reflects and refracts
D Light is absorbed completely
Correct Answer:  B. Light undergoes total internal reflection
Explanation:

At critical angle θ_c, refracted ray becomes parallel to the interface. Beyond this angle, no refraction occurs; light completely reflects back into the denser medium (total internal reflection). This principle enables fiber optics.

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Q.165 Hard Physics
A copper wire is stretched elastically. Which property is NOT affected?
A Young's modulus
B Electrical resistivity
C Length
D Cross-sectional area
Correct Answer:  A. Young's modulus
Explanation:

Young's modulus is a material property independent of the wire's dimensions or elastic deformation state. It depends only on the material composition and atomic structure, not on physical changes.

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Q.166 Easy Physics
Which of the following statements about velocity is correct?
A Velocity is a scalar quantity that can never be negative
B Velocity is a vector quantity that includes both magnitude and direction
C Velocity and speed are always equal in magnitude
D Velocity remains constant in circular motion
Correct Answer:  B. Velocity is a vector quantity that includes both magnitude and direction
Explanation:

Velocity is a vector quantity with both magnitude and direction, unlike speed which is scalar. Velocity can be negative, and in circular motion, velocity constantly changes direction.

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Q.167 Easy Physics
A ball is thrown vertically upward with an initial velocity of 20 m/s. What is the maximum height reached? (Take g = 10 m/s²)
A 10 m
B 20 m
C 30 m
D 40 m
Correct Answer:  B. 20 m
Explanation:

Using v² = u² - 2gh, where final velocity v = 0, u = 20 m/s, g = 10 m/s². Therefore, 0 = 400 - 20h, giving h = 20 m.

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Q.168 Easy Physics
Which law of motion states that the acceleration of an object is directly proportional to the net force applied and inversely proportional to its mass?
A Newton's First Law
B Newton's Second Law
C Newton's Third Law
D Law of Universal Gravitation
Correct Answer:  B. Newton's Second Law
Explanation:

Newton's Second Law: F = ma, where acceleration is directly proportional to force and inversely proportional to mass.

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Q.169 Easy Physics
A 2 kg object accelerates at 5 m/s² when a net force is applied. What is the magnitude of the net force?
A 2.5 N
B 5 N
C 10 N
D 20 N
Correct Answer:  C. 10 N
Explanation:

Using F = ma, F = 2 × 5 = 10 N. This is a direct application of Newton's Second Law.

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Q.170 Medium Physics
Two identical objects moving with velocities v and 2v collide and stick together. What fraction of kinetic energy is lost?
A 1/3
B 2/3
C 1/2
D 2/5
Correct Answer:  B. 2/3
Explanation:

Initial KE = ½m(v)² + ½m(2v)² = 2.5mv². Final velocity = 3v/2 (by momentum conservation). Final KE = ½(2m)(3v/2)² = 2.25mv²/4 = 0.84mv². Loss = 2.5 - 0.84 = 1.66, which is 2/3 of initial KE.

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