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

Subtopic:  Mass-Energy Equivalent |
 61%
From NCERT
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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

Subtopic:  Mass-Energy Equivalent |
 79%
From NCERT
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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

Subtopic:  Radioactivity (OLD NCERT) |
 78%
From NCERT
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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

Subtopic:  Radioactivity (OLD NCERT) |
 86%
From NCERT
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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

Subtopic:  Radioactivity (OLD NCERT) |
 87%
From NCERT
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The nucleus C612 absorbs an energetic neutron and emits a beta particle β-. The resulting nucleus is 

1. C714

2. N713 

3. B513 

4. C613

Subtopic:  Types of Decay |
 69%
From NCERT
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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

Subtopic:  Mass-Energy Equivalent |
 81%
From NCERT
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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

Subtopic:  Nuclear Binding Energy | Mass-Energy Equivalent |
 87%
From NCERT
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The counting rate observed from a radioactive 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

Subtopic:  Radioactivity (OLD NCERT) |
 68%
From NCERT
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If N0 is the original mass of the substance of half life period T1/2= 5 years, then the amount of substance left after 15 years is [AIEEE 2012]

1. N0/8 

2. N0/16

3. N0/2

4. N0/4

Subtopic:  Radioactivity (OLD NCERT) |
 88%
From NCERT
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