Light energy emitted by stars is due to

(1) Breaking of nuclei                          (2) Joining of nuclei       

(3) Burning of nuclei                            (4) Reflection of solar light

Concept Questions :-

Mass-energy equivalent
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The constituents of atomic nuclei are believed to be [1991]

(1) neutrons and protons

(2) protons only

(3) electrons and protons

(4) electrons, protons and neutrons

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The half-life of radium is about 1600 yr. of 100 g of radium existing now, 25 g will remain unchanged after [2004]

(1) 4800 yr         (2) 6400 yr           (3) 2400 yr           (4) 3200 yr

Concept Questions :-

Radioactivity
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The binding energy of deuteron is 2.2 MeV and that of H24e is 28 MeV. If two deuterons are fused to form one H24e, then the energy released is [2006]

(1) 25.8 MeV        (2) 23.6 MeV           (3) 19.2 MeV          (4) 30.2 MeV

Concept Questions :-

Nuclear binding energy
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Half-life of a radioactive substance is 12.5 h and its mass is 256 g. After what time, the amount of remaining substance is 1 g? [2001]

(1) 75 h          (2) 100 h            (3) 125 h          (4) 150 h

Concept Questions :-

Radioactivity
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A radioactive substance disintegrates 1/64 of initial value in 60 s. The half-life of this substance is

(1) 5 s         (2) 10 s          (3) 30 s          (4) 20 s

Concept Questions :-

Radioactivity
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The nucleus C126 absorbs an energetic neutron and emits a beta particle β-. The resulting nucleus is 

(1) N147          (2) N137         (3) B135             (4) C136

Concept Questions :-

Mass-energy equivalent
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If in a nuclear fusion  process, the masses of the fusion nuclei be m1 and m2 and the mass of the resultant nucleus be m3, then [2004]

(1) m3=m1+m2                     (2) m3=m1-m2

(3) m3<m1+m2                  (4) m3>m1+m2

Concept Questions :-

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The nuclei of which one of the following pairs of nuclei are isotones? [2005]

(1) S34e74, G31a71                  (2) M42o92, Z40r92

(3) S38r84, S38r86                    (4) C20a40, S3216

Concept Questions :-

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The counting rate observed from a radio active source at t = 0 second was 1600 counts per second and at t = 8 seconds it was 100 counts per second. The counting rate observed, as counts per second, at t = 6 seconds will be

(1) 400         (2) 300         (3) 200        (4) 150

Concept Questions :-

Radioactivity
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