The Weber (Wb) is the SI unit of magnetic flux, defined as Tesla × meter². 1 Wb = 1 T·m².
Q.82Medium
A transformer has 100 turns in the primary coil and 500 turns in the secondary coil. If the primary voltage is 220V, what is the secondary voltage assuming 100% efficiency?
Answer: C
Using transformer equation: Vₛ/Vₚ = Nₛ/Nₚ. Vₛ = 220 × (100500) = 220 × 5 = 1100 V.
Q.83Medium
Which statement about alpha decay is correct?
Answer: A
An alpha particle is a helium-4 nucleus (₂He⁴) with 2 protons and 2 neutrons. Alpha decay decreases atomic number by 2 and mass number by 4. Alpha particles have low penetration power.
Q.84Medium
A nucleus undergoes beta decay. Which particle is emitted along with an antineutrino?
Answer: B
In beta-minus decay, a neutron converts to a proton, emitting an electron (beta particle) and an antineutrino. This increases atomic number by 1.
Q.85Medium
Which phenomenon explains the blue color of the sky?
Answer: B
Rayleigh scattering causes shorter blue wavelengths to scatter more effectively than longer red wavelengths when sunlight passes through the atmosphere, making the sky appear blue.
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Q.86Medium
A 1000 W heater operates at 250 V. What is its resistance?
Answer: C
Using P = V²/R, we get R = V²/P = (250)²/1000 = 100062500 = 62.5 Ω.
Q.87Medium
A concave mirror has a focal length of 10 cm. An object is placed 5 cm from the mirror. What type of image is formed?
Answer: B
When object distance (5 cm) < focal length (10 cm), the object is between the mirror and focus. A concave mirror forms a virtual, erect, and magnified image in this case.
Q.88Medium
Two resistances of 10 Ω and 20 Ω are connected in parallel. What is the equivalent resistance?
A sound wave has a frequency of 440 Hz and travels at 330 m/s in air. What is its wavelength?
Answer: A
Using v = fλ, where v = 330 m/s and f = 440 Hz. λ = v/f = 440330 = 0.75 m.
Q.90Medium
When a spring is compressed by 0.1 m, the elastic potential energy stored is 5 J. What is the spring constant?
Answer: B
Elastic potential energy E = (21)kx². 5 = (21)k(0.1)². 5 = 0.005k. k = 1000 N/m.
Q.91Medium
Which of the following correctly describes the photoelectric effect?
Answer: A
The photoelectric effect occurs when light of frequency greater than or equal to the threshold frequency strikes a metal surface, causing electron emission. It demonstrates the particle nature of light.
Q.92Medium
A moving object has kinetic energy K. If its velocity is doubled, what will be its new kinetic energy?
Answer: B
Kinetic energy KE = (21)mv². When velocity is doubled: KE' = (21)m(2v)² = (21)m(4v²) = 4 × (21)mv² = 4K.
Q.93Medium
Which law of thermodynamics explains why heat cannot spontaneously flow from a colder body to a hotter body?
Answer: B
The Second Law of Thermodynamics states that entropy of an isolated system increases or remains constant. Heat spontaneously flows from hot to cold, not vice versa, establishing the direction of processes.
Q.94Medium
A ball is thrown vertically upward with initial velocity 20 m/s. What maximum height does it reach? (g = 10 m/s²)
Answer: B
At maximum height, v = 0. Using v² = u² - 2gh: 0 = 20² - 2(10)h. 20h = 400. h = 20 m.
Q.95Medium
Two capacitors of 2 μF and 3 μF are connected in series. What is the equivalent capacitance?
Answer: B
For capacitors in series: 1/C = 1/C₁ + 1/C₂ = 21 + 31 = 65. Therefore C = 56 = 1.2 μF.
Q.96Medium
A body moves in a circle of radius 5 m with constant speed 10 m/s. What is the centripetal acceleration?
