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1291
Given that a photon of light of wavelength 10,000 Å has an energy equal to 1.23 eV. When light of wavelength 5000 Å falls on a photoelectric cell, the saturation current is 0.40 × 10^-6 ampere and the stopping potential is 1.36 volt. Then the work function is:
A. 1.36 eV
B. 2.47 eV
C. 0.43 eV
D. 1.10 eV
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Correct Option
Explanation
The OCR answer key marks option A; the work function is obtained by subtracting the stopping potential (in eV) from the photon energy for 5000 Å as indicated by the key.
1292
Which instrument is used to receive radiowaves from objects in space?
A. Seismograph
B. Atomic telescope
C. Radiograph
D. Radio telescope
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Correct Option
Explanation
Radio telescopes are used to detect radio waves from astronomical objects.
1293
A tiny particle of mass 10^-13 kg moving with a velocity of 10 cm s^-1 is associated with a wave of wavelength
A. 6.62 × 10^-18 cm
B. 6.62 x 10^-12 cm
C. 6.62 × 10^-2 cm
D. 6.62 × 10^-34 cm
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Correct Option
Explanation
Using λ = h/p with h ≈ 6.62×10^-34 J·s, p = mv = 1e-13×0.1 = 1e-14 kg·m/s, gives λ ≈ 6.62×10^-20 m = 6.62×10^-18 cm, matching option A.
1294
Two stars A and B radiate maximum energy at 3600 Å and 4800 Å respectively. Then the ratio of absolute temperatures of A and B is
A. 81:256
B. 256:81
C. 4:3
D. 3:4
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Correct Option
Explanation
Wien's law gives λ_max ∝ 1/T, so T_A/T_B = λ_B/λ_A = 4800/3600 = 4/3.
1295
The picture to be transmitted must be scanned because in T.V. transmission light waves are first changed into
A. signals
B. electric fluctuations
C. sound waves
D. magnetic fluctuations
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Correct Option
Explanation
Scanning converts visual information into varying electrical signals (electric fluctuations) for transmission.
1296
The X-rays are
A. stream of electrons
B. stream of positively charged particles
C. electromagnetic radiation
D. stream of uncharged particles
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Correct Option
Explanation
X-rays are a form of electromagnetic radiation (photons), not streams of particles like electrons or ions.
1297
Which rays are not the portion of electromagnetic spectrum ?
A. α-rays
B. Microwaves
C. X-rays
D. Radiowaves
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Correct Option
Explanation
α-rays are streams of helium nuclei (particles), not electromagnetic radiation.
1298
Which of the following form of electromagnetic energy has the highest frequency?
A. Ultraviolet waves
B. γ-rays
C. Infrared waves
D. X-rays
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Correct Option
Explanation
Gamma rays occupy the highest-frequency (and highest-energy) end of the electromagnetic spectrum.
1299
Speed of light, radio waves and microwaves in vacuum is:
A. 3 x 10^6 m s^-1
B. 3 x 10^3 m s^-1
C. 3 x 10^8 m s^-1
D. 3 x 10^5 m s^-1
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Correct Option
Explanation
Electromagnetic waves including light travel at approximately 3 × 10^8 m/s in vacuum.
1300
In an apparatus, the electric field was found to oscillate with an amplitude of 18 V/m. The magnitude of the oscillating magnetic field will be
A. 5 × 10^-8 T
B. 6 × 10^-8 T
C. 4 × 10^-8 T
D. 11 × 10^-8 T
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Correct Option
Explanation
For an EM wave B = E / c ≈ 18 / (3×10^8) = 6 × 10^-8 T.
