Enter Einstein!

Q. When the light of frequency $2{\nu }_0$ (where ${\nu }_0$ is a threshold frequency) is incident on a metal plate, the maximum velocity of electrons emitted is $v_1$. When the frequency of the incident radiation is increased to $5{\nu }_0$, the maximum velocity of electrons emitted from the same plate is $v_2$. The ratio of $v_1$ to $v_2$ is

1. 1 : 2
2. 1 : 4
3. 4 : 1
4. 2 : 1

Q.

The work function for tungsten and sodium are 4.5 eV and 2.3 eV respectively. If the threshold wavelength $\lambda$ for sodium is $5460\stackrel{\circ }{A}$ the value of $\lambda$ for tungsten is

1. $5893\stackrel{\circ }{A}$

2. $10683\stackrel{\circ }{A}$

3. $2791\stackrel{\circ }{A}$

4. $528\stackrel{\circ }{A}$

Q.

Write about Albert Einstein in 200-300 words

Q. The threshold wavelength for a metal having work function $W_0$ is ${\lambda }_0$. What is the threshold wavelength for a metal whose work function is $\frac{W_0}{2}$?

1. $2{\lambda }_0$
2. $\frac{{\lambda }_0}{2}$
3. $\frac{{\lambda }_0}{4}$
4. $4{\lambda }_0$

Q.

In Davisson-German experiment, observed value of de-Broglie’s wavelength is 0.165$nm$ whereas theoretical value is 0.166$nm$. Choose the correct reason for lower experimental value.

1. Error in observation of angle at which maxima of intensity of diffracted electron occurs.

2. Temperature of nickel crystal is more than the ambient temperature

3. Electron speed inside the crystal is more than $\sqrt{\left(\frac{2qV}{m}\right)}$ and no account is made to calculate this increase of speed.

4. Electron behave like waves in this experiment.

Q. ntif the potential energy (PE) of hydrogen electron is -3.02eV then in which of the following excited level is electron presentn nt(a) 1stn nt(b) 2ndn nt(c) 3rdn nt(d) 4thn

Q. 61. An electric field exists in space as E=2+3j+0k. Find potential difference Va-Vb between points A(2, 2, 0) and B(1, 1, 0)

Q.

A difference of 2.3 eV separates two energy levels in an atom. What is the frequency of radiation emitted when the atom makes a transition from the upper level to the lower level?

Q.

Find the total energy of the particle executing linear SHM and show graphically the variation of P.E and K.E with respect to position.

Q. Light rays of wavelengths $6000\mathring{A}$ and of Photon intensity $39.6{\text{W m}}^2$ is incident on a metal surface. If only one percent of photons incident on the surface, emit photo electrons, then the number of electrons emitted per second per unit area from the surface will be-
[Use $h=6.64\times {10}^{-34}\text{J s}$]

1. $12\times {10}^{18}$
2. $12\times {10}^{17}$
3. $12\times {10}^{16}$
4. $12\times {10}^{15}$

Q.

Einstein's photoelectric equation states that $E_k=hv-\varphi$. In this equation $E_k$ refers to

1. Kinetic energy of all the emitted electrons

2. Mean kinetic energy of the emitted electrons

3. Maximum kinetic energy of the emitted electrons

4. Minimum kinetic energy of the emitted electrons

Q.

If the wavelength of incident light changes from $300nmto400nm$, then find the change in sloping potential. If the work function of metal$=2.5eV$?

1. $1.03eV$

2. $2.10eV$

3. $1.85eV$

4. $2.03eV$

Q.

The separation betweenthe consecutive darki fringes in a young's double slit experiment is 1.0 mm. The screen is placed at a distance of 2.5 m from the slits an the separation between the slits is 1.0 mm. Calculate the wavelength of light used for the experiment.

Q.

If the threshold wavelength for sodium is $5420\stackrel{\circ }{A}$, then the work function of sodium is

1. 2.28 eV

2. 1.14 eV

3. 4.58 eV

4. 0.23 eV

Q.

(a) An X-ray tube produces a continuous spectrum of radiation with its short wavelength end at 0.45 Å. What is the maximum energy of a photon in the radiation?

(b) From your answer to (a), guess what order of accelerating voltage (for electrons) is required in such a tube?

Q.

What is meant by the photoelectric effect?

Q.

A 100 W sodium lamp radiates energy uniformly in all directions. The lamp is located at the centre of a large sphere that absorbs all the sodium light which is incident on it. The wavelength of the sodium light is 589 nm. (a) What is the energy per photon associated with the sodium light? (b) At what rate are the photons delivered to the sphere?

Q.

.A capacitor is charged to potential V and is disconnected . A dielectric of dielectric
constant 4 is inserted filling the whole space between the plates. How do the following
change? –Capacitance, potential difference, Field between the plates, energy stored by
the capacitors.

Q. According to Einstein, the mass of an object increases as its speed increases. This increase in mass comes from :

1. nuclear binding energy.
2. electron energy in the ground state.
3. potential energy being converted into mass by $E=m{c}^2$
4. the lower pressure on the mass.
5. kinetic energy being converted into mass by $E=m{c}^2$

Q.

Explain Conservation of Energy.

Q. (a) Describe briefly three experimentally observed features in the phenomenon of photoelectric effect.
(b) Discuss briefly how wave theory of light cannot explain these features.

Q.

Einstein got Nobel prize on which of the following works

1. Mass-energy relation

2. Special theory of relativity

3. Photoelectric equation

4. (a) and (b) both

Q.

The kinetic energy of photoelectrons depends on?

1. The intensity of incident light

2. The sum of threshold frequency and frequency of incident light

3. The ratio of of threshold frequency and frequency of incident light

4. The difference of threshold frequency and frequency of incident light

Q. State two ways by which electrons can be made to leave the metal surface.

Q. Write Einstein's equation of photoelectric effect. Give Einsteins explanation of photoelectric effect.

Q.

Assertion : The electron will be ejected from a hydrogen atom when electron beam of kinetic energy $10.6eV$ falls on it.

Reason : The difference between n₁ and n₂ is $10.2eV$

1. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion

2. If both Assertion & Reason are True & the Reason is not a correct explanation of the Assertion

3. If Assertion is True but the Reason is False

4. If both Assertion & Reason are false

Q.

Given below are some famous numbers associated with electromagnetic radiations in different contexts in physics. State the part of the electromagnetic spectrum to which each belongs.

(a) 21 cm (wavelength emitted by atomic hydrogen in interstellar space).

(b) 1057 MHz (frequency of radiation arising from two close energy levels in hydrogen; known as Lamb shift).

(c) 2.7 K [temperature associated with the isotropic radiation filling all space-thought to be a relic of the ‘big-bang’ origin of the universe].

(d) 5890 Å - 5896 Å [double lines of sodium]

(e) 14.4 keV [energy of a particular transition in ⁵⁷Fe nucleus associated with a famous high resolution spectroscopic method

(Mössbauer spectroscopy)].

Q.

Light of frequency 7.21 × 10¹⁴ Hz is incident on a metal surface. Electrons with a maximum speed of 6.0 × 10⁵ m/s are ejected from the surface. What is the threshold frequency for photoemission of electrons?

Q. The graph between the stopping potential $\left(V_0\right)and\left(1/\lambda \right)$ is shown in the Fig. ${\varphi }_1,{\varphi }_{2}and{\varphi }_3$ are work functions. Then, which of the following is/are correct?

1. ${\varphi }_1:{\varphi }_2:{\varphi }_3=1:2:4$
2. ${\varphi }_1:{\varphi }_2:{\varphi }_3=4:2:1$
3. tan $\theta \alpha$ (hc)/e
4. Ultraviolet light can be used to emit photoelectrons from metal 2 and metal 3 only

Q. In photoelectric effect on increasing the collector plate potential (accelerating potential) the photoelectric current

1. Keeps increasing
2. Increases first and then becomes constant
3. Remains constant irrespective of potential value
4. Decreases continuously