Atoms Test

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Atoms Test - 22

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Weekly Quiz Competition

Question 1
1 / -0

When electron remains between orbits, its momentum is :

A
quantized

B
dequantized

C
emitted

D
changed always

Solution

A
The first postulate of Bhor theory is that the orbital momentum of the electron is quantized ie, L = mvr = nh where h is Drac constant.
Question 2
1 / -0

Number of spectral lines in hydrogen atom is

A
$$8$$

B
$$6$$

C
$$15$$

D
$$\infty$$

Solution

Number of spectral lines in hydrogen atom $$\infty$$.
Question 3
1 / -0

When electron changes its orbit from outer to inner energy is :

A
absorbed

B
released

C
no change

D
remains constant

Solution

Released
When electron emits energy it becomes stable and jump from higher energy level (outer shell) to lower energy level (inner shell).
Question 4
1 / -0

When an electron jumps from its orbit to another orbit, energy is :

A
emitted

B
absorbed

C
both absorbed and emitted

D
depends on the energy levels of the orbits

Solution

When an electron jumps from lower energy level to higher energy level it absorbs energy and when it jumps from higher energy level to lower energy level it emits energy.
So whether the electron emits or absorbs energy depends on the energy levels of the orbits.
Question 5
1 / -0

Orbits in which electrons move according to Bohr are :

A
elliptical

B
cylindrical

C
circular

D
oval

Solution

C. Circular
First electron shell which is closest to the orbit to the nucleus, called the 1s orbit can hold up two two electrons. This orbit is equivalent to the innermost electron shell of the Bhor model of atom. It is called the orbital because it is spherical around the nucleus.
Question 6
1 / -0

In a laser tube, all the photons

A
have same wavelength

B
have same energy

C
move in same direction

D
move with same speed.

Solution

The photon produced in a laser move at the speed of light and it is constant for all the photons. $$(c = 3\times10^8 m/s)$$.

Practically the light from the laser has slight variations in their wavelength and the frequency. So, they cannot be same.
Question 7
1 / -0

According to the quantum theory of light, the energy of light is carried in discrete units called

A
alpha particles

B
photoelectrons

C
protons

D
photons

Solution

According to the quantum theory of light, energy of light is carried in discrete units called photons.
Question 8
1 / -0

According to Bohr's model of hydrogen atom, relation between principal quantum number n and radius of stable orbit is

A
$$r \propto \frac{1}{n}$$

B
$$r \propto n$$

C
$$r\propto\frac{1}{n^2}$$

D
$$r\propto n^2$$

Solution

Let an electron (mass m), is revolving around nucleus of a hydrogen atom in an orbit of radius $$r$$ with velocity $$v$$. Electron gets centripetal force to revolve, from the electrostatic attraction force between electron and nucleus,
$$\dfrac{mv^{2}}{r}=\dfrac{e\times e}{4\pi\varepsilon_{0}r^{2}}$$ (for H- atom, $$Z=1$$ hence charge on nucleus is $$=e$$)
  $$mv^{2}=\dfrac{e^{2}}{4\pi\varepsilon_{0}r}$$ ...................eq1

According to Bohr's model, angular momentum of electron :
$$mvr=\dfrac{nh}{2\pi}$$ ..................eq2

Now, squaring eq2 and dividing by eq1, we get
  $$\dfrac{mv^{2}r^{2}}{mv^{2}}=\dfrac{n^{2}h^{2}4\pi\varepsilon_{0}r}{4\pi^{2}e^{2}}$$

  $$r=\dfrac{n^{2}h^{2}\varepsilon_{0}}{\pi me^{2}}$$

which gives $$r\propto n^{2}$$
Question 9
1 / -0

In an atom an electron excites to the fourth orbit.When it jumps back to the energy level one a spectrum is formed. Total number of spectral lines in this spectrum would be

A
3

B
4

C
5

D
6

Solution

The relation to find number of spectral lines is $$\frac{({{n}_{2}}-{{n}_{1}})({{n}_{2}}-{{n}_{1}}+1)}{2}$$

Here transition is from n = 4 to n = 1

So, number of spectral lines = $$\frac{3\times 4}{2}=6$$

Hence, there are 6 spectral lines.
Question 10
1 / -0

When an alpha particle is emitted from a radioactive source.

A
Its atomic number increases by $$4$$

B
Its atomic number decreases by $$2$$

C
Its atomic number increases by $$2$$

D
It atomic number decreases by $$4$$

Solution

When an alpha particle is emitted from a radioactive source or substance, its atomic number decreases by 2 and its atomic mass decreases by 4, which is same as that of helium ion.

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Atoms Test - 22

Result

Atoms Test - 22

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Question 1

quantized

dequantized

emitted

changed always

Solution

Question 2

$$8$$

$$6$$

$$15$$

$$\infty$$

Solution

Question 3

absorbed

released

no change

remains constant

Solution

Question 4

emitted

absorbed

both absorbed and emitted

depends on the energy levels of the orbits

Solution

Question 5

elliptical

cylindrical

circular

oval

Solution

Question 6

have same wavelength

have same energy

move in same direction

move with same speed.

Solution

Question 7

alpha particles

photoelectrons

protons

photons

Solution

Question 8

$$r \propto \frac{1}{n}$$

$$r \propto n$$

$$r\propto\frac{1}{n^2}$$

$$r\propto n^2$$

Solution

Question 9

3

4

5

6

Solution

Question 10

Its atomic number increases by $$4$$

Its atomic number decreases by $$2$$

Its atomic number increases by $$2$$

It atomic number decreases by $$4$$

Solution

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