BITSAT 2019 Physics Modern Physics Revision Quiz 1

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Question 1

A sample contains 10^-2 kg each of the two substances A and B with half-lives 4 s and 8 s respectively. Their atomic weights are in the ratio of 1:2, the amounts of A and B after an interval of 16s are

• AA=0.625×10^-4 kg, B=0.25×10^-3 kg
• BA=0.25×10^-3 kg, B=0.625×10^-4 kg
• CA=2.5×10^-3 kg, B=6.25×10^-4 kg
• DA=6.25×10^-4 kg, B=2.5×10^-3 kg

Question 2

Usually laser beams are used to measure long distance because

• Athey are coherent
• Bthey are monochromatic
• Cthey are highly polarised
• Dthey have high degree of parallelism

Question 3

Which of the following process represents γ–decay?

• A
• B
• C
• D

Question 4

The radioisotope of carbon-14 is maintain a fixed proportion in a tree by exchanging C with the atmosphere. After it dies, exchange ceases and proportion of Carbon-14 decreases continuously in the form of β-decay with half life of 5500years. Estimate the age of dead tree whose present activity is one-third of its initial activity.

• A8719 years
• B8700 years
• C8725 years
• D8711 years

Question 5

In a sample there are 15% undecayed radioactive nuclei present at any instant of time. After 20 minutes later, the number of undecayed nuclei reduces to 7.5%. Calculate the mean life of nuclei.

• A30 minutes
• B28.86 minutes
• C35.45 minutes
• D40 minutes

Question 6

In the hydrogen atom, the ratio of wavelength of the Lyman-β transition to Balmer-β transition is

• A
• B
• C
• DNone of these

Question 7

Given that the binding energies per nucleon of a deuteron and alpha particle are 1.1 MeV and 7 MeV respectively, the energy released in the reaction is about

• A18.4 MeV
• B32.5 MeV
• C23.6 MeV
• D29.5 MeV

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