Atoms Test

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Atoms Test - 25

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Weekly Quiz Competition

Question 1
1 / -0

When the particle and its anti-particle unite, the result is

A
A heavier particle

B
Two or more smaller particles

C
Photons

D
Partly matter and partly photons
Question 2
1 / -0

In the Geiger-Marsden experiment, the force that scatters particles is

A
nuclear force

B
coulomb force

C
both A and B

D
gravitational force

Solution

Coulomb force is responsible for scattering of particles. When the alpha particles (positive in charge) get closer to the nucleus, which is positive in charge, they get repelled through various angles.
Question 3
1 / -0

The force experienced by the cathode rays when they pass through a uniform electric field of intensity $$\bar{E}$$ is:

A
in the direction of the electric field

B
in the direction opposite to that of the electric field

C
at right angles to the electric field

D
zero, because cathode rays do not have any charge

Solution

Cathode particles are negatively charged
$$\therefore F_E = -q \vec{E} $$
Force is opposite to the direction of electric field
Question 4
1 / -0

Cathode rays are made to pass between the poles of a magnet as shown in figure. The effect of magnetic field is

A
To deflect them towards the south pole

B
To deflect them perpendicular to the plane of the paper and towards the observer

C
To deflect them towards the north pole

D
To increase the velocity of the rays

Solution

Force will be perpendicular and outside to the plane of the paper
Question 5
1 / -0

The angular momentum of the $$\alpha -$$particles which are scattered through large angles by the heavier nuclei, is conserved because

A
of the nature of repulsive forces

B
the kinetic energy is conserved

C
the potential energy is conserved

D
there is no external torque

Solution

The angular momentum of $$\alpha$$ particles is conserved because there is no external torque.
Question 6
1 / -0

An electron makes transition from $$n= 3 , n=1$$ state in a hydrogen atom. The different possible number of photons that can be emitted is :

A
$$1$$

B
$$2$$

C
$$3$$

D
$$6$$

Solution

For transition from $$n=3$$ to $$n=1$$
Possible number of photons $$=\ ^3C_2$$$$=\dfrac{3!}{(3-2)!2!}$$$$=\dfrac{3\times 2\times 1}{1\times 2\times 1}=3$$
Question 7
1 / -0

In the lowest energy level of hydrogen atom, electron has an angular momentum equal to:

A
$$\dfrac{\pi }{h}$$

B
$$\dfrac{h}{\pi }$$

C
$$\dfrac{h}{2\pi }$$

D
$$\dfrac{2\pi }{h}$$

Solution

The angular momentum$$ L$$ $$=m_{e}vr$$ is on integer multiple of $$\dfrac{h}{2\pi }$$

$$mvr=\dfrac{nh}{2\pi}$$

For, $$n=1$$

$$mvr=\dfrac{h}{2\pi}$$
Question 8
1 / -0

The ionization energy of a hydrogen-like ion $$A$$ is greater than that of another hydrogen-like ion $$B$$. Let $$u$$ and $$E$$ represent the speed of the electron and energy of the atom respectively in the ground state. Then,

A
$$r_{A}> r_{B}$$

B
$$u_{A}> u_{B}$$

C
$$E_{A}> E_{B}$$

D
$$L_{A}> L_{B}$$

Solution

We know

$$E=-13.6\dfrac{Z^{2}}{n^{2}}eV$$

So Ionization energy $$=13.6\dfrac{Z^{2}}{n^{2}}eV$$

given, $$IE_{A}> IE_{B},$$ so $$E_{A}< E_{B}$$

that means $$Z_{A}> Z_{B}$$

Now $$u \propto \dfrac{Z}{n}$$

$$u_{A}> u_{B}$$
Question 9
1 / -0

In Rutherford's experiment the number of $$\alpha$$ particles scattered through an angle $$60^o$$ is $$112$$ per minute, then the number of $$\alpha$$ particles scattered through an angle of $$90^{0}$$ per minute by the same nucleus is:

A
$$28$$ per minute

B
$$112$$ per minute

C
$$12.5$$ per minute

D
$$7$$ per minute

Solution

In Rutherford's experiment the number of particles scattered through an angle $$\theta$$ per minute is given by:
$$N \propto \dfrac{Z^2}{Sin^4(\theta /2)}$$

According to the question: the number of particles scattered through an angle $$60^o$$ is 112 per minute. So,
$$112 \propto \dfrac{Z^2}{Sin^4(60 /2)}$$------ (1)

And, lets assume the number of particles scattered through an angle $$90^o$$ is N' per minute
$$N' \propto \dfrac{Z^2}{Sin^4(90 /2)}$$------(2)

Using (1) and (2),
$$\dfrac{N'}{112} \propto \dfrac{Sin^4(60 /2)}{Sin^4(90 /2)}$$

$$N'=28$$
Question 10
1 / -0

The radius of hydrogen atom, when it is in its second excited state ,becomes $$\underline{\hspace{0.5in}}$$ its ground state radius.

A
half

B
double

C
four times

D
nine times

Solution

$$r=\dfrac{a_{0}n^{2}}{Z}$$
$$r_{1}$$ ( ground state ) $$={a_{0}}(1)^{2}$$
$$=a_{0}$$
$$r_{2}$$ ( 2nd excited state ) $$=a_{0}(3)^{2}$$
$$=9a_{0}$$

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Re-Attempt Weekly Quiz Competition

Atoms Test - 25

Result

Atoms Test - 25

Score

-

Rank

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SHARING IS CARING

Question 1

A heavier particle

Two or more smaller particles

Photons

Partly matter and partly photons

Question 2

nuclear force

coulomb force

both A and B

gravitational force

Solution

Question 3

in the direction of the electric field

in the direction opposite to that of the electric field

at right angles to the electric field

zero, because cathode rays do not have any charge

Solution

Question 4

To deflect them towards the south pole

To deflect them perpendicular to the plane of the paper and towards the observer

To deflect them towards the north pole

To increase the velocity of the rays

Solution

Question 5

of the nature of repulsive forces

the kinetic energy is conserved

the potential energy is conserved

there is no external torque

Solution

Question 6

$$1$$

$$2$$

$$3$$

$$6$$

Solution

Question 7

$$\dfrac{\pi }{h}$$

$$\dfrac{h}{\pi }$$

$$\dfrac{h}{2\pi }$$

$$\dfrac{2\pi }{h}$$

Solution

Question 8

$$r_{A}> r_{B}$$

$$u_{A}> u_{B}$$

$$E_{A}> E_{B}$$

$$L_{A}> L_{B}$$

Solution

Question 9

$$28$$ per minute

$$112$$ per minute

$$12.5$$ per minute

$$7$$ per minute

Solution

Question 10

half

double

four times

nine times

Solution

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