Structure Of Atom Important MCQ’s for Exams:

Positive rays are produced in discharge tube:

1.  From cathode surface

2. From anode surface

3.By ionization of gas molecules

4. Both a & b

Answer )By ionization of gas molecules

Brief Explanation :

Goldstein found that positive rays consists of positively charged ions .

The ions are produced in discharge tube when cathode rays collide with the gas molecules and ionize them sharp .

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William Crook concluded from pin wheel experiment that cathode rays have:

1.Momentum and energy

2.Positive charge

3.Cast shadow

4.Deflect in magnetic field

Answer ) Momentum and energy

Brief Explanation :

William Crook observe that cathode rays can rotate a pin wheel place in their way.

He concluded that cathode rays are bunch of particles having definite mass and velocity.

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A visible ray of highest frequency is:

1.Red

2.Violet

3.Infra red

4.Ultraviolet

Answer )Violet   

Brief Explanation :

A visible spectrum consists of seven colors  (VIBGYOR).

i.e Violet (400-420 nm), indigo (420-460nm) ,blue(460-510 nm) , green (510 -580 nm), yellow (580-600 nm),orange (600-630 nm)& red ((630-750 nm).

Frequency is inversely related to wavelength of radiation. Higher the frequency, shorter is the wavelength and vice versa.

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The decreasing order of wavelengths when energy of radiation A > C> B:

1.A > C> B

2.B > C> A

3.A > B> C

4. C > B> A

Answer ) 2. B > C> A

Brief Explanation :

We know that frequency is directly proportional to energy and inversely proportional to wavelength of a radiation. A radiation of greater energy has shorter wavelength and vice versa.

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In continuous spectrum:

1.Some wavelengths are missing

2. No wavelengths are missing

3.Dark spaces separate bright lines

4.Additional wavelengths are observed   

   Answer )    No wavelengths are missing

Brief Explanation :

In continuous spectrum , all wavelengths of incident light are present and no wavelength is missing. Different colors are diffused into each other and not separated by dark spaces .For example, rainbow seen in the sky .

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A band of colors of an oil film on the Water surface is an example of :

1.Continuous spectrum

 2. Discontinuous spectrum

 3.Band spectrum

4. Line spectrum

Answer )Continuous spectrum

Brief Explanation :

A band of colors of an oil film on the water surface is an example of continuous spectrum in which different colors are diffused into each other and not separated by dark spaces.

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Bohr’s model helps to explain:

1.Photoelectric effect

2.Zeeman effect

3.Stark effect

4.Stability and Line spectrum

Answer )      Stability and Line spectrum

Brief Explanation :

Bohr’s model helps  to explain the stability and line spectrum of an atom.

According to Bohr’s model , an electron neither loses or gain energy until it remains in the same shell .Moreover, an atom emits or absorbs energy at intervals and not continuously, hence an atom has line spectrum.

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An electronic level that allows only absorption and not emission of energy :

1.1s

2.2s

3.2p

4.3s

Answer ) 1s

Brief Explanation :

The lowest energy level is 1s. An electron in 1s- level can absorb energy to jump into higher energy level.

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When an electron falls from higher into second energy level in H-atom, the emitted radiations are:

1. Ultraviolet

2.Infra-red

3.Visible

4.X-rays

Answer )  Visible

Brief Explanation :

Balmer studied a series of spectral lines produced when an electron jumps from higher energy levels (n2 = 3,4,5,6,7 ) into second energy level ( n1= 2).He observed that the emitted radiations have energy, frequency and wavelength in the visible region.

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The frequency of X-rays produced in X-rays tube increase with an increase in:

1.  Size of cathode

2.Atomic number of cathode

3.Size of anti-cathode

4.Atomic number of anti- cathode

Answer ) Atomic number of anti- cathode

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