SSC CGL Science – Modern Physics, Electronics & Everyday Devices – Level 3 · Challenge

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SSC CGL Science – Modern Physics, Electronics & Everyday Devices – Level 3 · Challenge – 8 questions, subject: General Science. Every question has the correct answer with a one-line explanation; tap "Show Answer". Free practice for TNPSC, UPSC, SSC, Bank and RRB exams – Shanmugam IAS Academy, Coimbatore.

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1.  
Th-232 (Z = 90) decays in a series to stable Pb-208 (Z = 82). The numbers of α and β⁻ particles emitted are:

Correct Answer: B [6 α and 4 β]

Explanation:

α = (232 − 208)/4 = 6; β = 2 × 6 − (90 − 82) = 4.

2.  
A 64 g sample of a radioactive isotope has a half-life of 5 minutes. After how long will only 2 g remain?

Correct Answer: A [25 minutes]

Explanation:

64 → 2 is 1/32 = 1/2⁵ → 5 half-lives × 5 min = 25 min.

3.  
A and B feed an OR gate. The OR output and A feed an AND gate whose output is Y. For all inputs, Y is equal to:

Correct Answer: C [A]

Explanation:

Truth table: Y = A·(A + B) gives 0, 0, 1, 1 = A.

4.  
Which pair of impurities will both make p-type silicon?

Correct Answer: B [Boron and gallium]

Explanation:

p-type needs group 13 dopants: B, Al, Ga, In.

5.  
In the fission ¹n + ²³⁵₉₂U → ¹⁴⁰₅₄Xe + ⁹⁴₃₈Sr + x ¹n, the value of x is:

Correct Answer: D [2]

Explanation:

Mass numbers: 236 = 140 + 94 + x → x = 2 (Z: 92 = 54 + 38 checks).

6.  
Statement-basedWhich is/are correct about nuclear fusion?
I. It needs extremely high temperature.
II. The hydrogen bomb is based on fusion.
III. Present nuclear power plants in India work on fusion.

Correct Answer: D [Only I and II]

Explanation:

Fusion needs millions of degrees and powers the H-bomb; all present power reactors use fission.

7.  
Match the followingMatch:
P. Induction cooktop Q. Solar cell R. Fluorescent tube S. Optical fibre
1. Photovoltaic effect 2. Total internal reflection 3. Eddy currents 4. UV light converted by a phosphor coating

Correct Answer: B [P-3, Q-1, R-4, S-2]

Explanation:

Cooktop – eddy currents; solar cell – photovoltaic; tube light – phosphor glows under UV; fibre – TIR.

8.  
A metal has a threshold wavelength of 620 nm. Light of wavelength 400 nm falls on it. The maximum kinetic energy of the emitted electrons is about (use E = 1240/λ):

Correct Answer: A [1.1 eV]

Explanation:

KE = 1240/400 − 1240/620 = 3.1 − 2.0 = 1.1 eV.

➤ Full notes, shortcuts and every answer explained – SSC CGL 2026 General Science book (₹149): www.shanmugamiasacademy.in/study-materials/ssc-cgl-general-science

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