CBSE 12th Term-2 Physics Solve Short Questions For Final Revision Before Exam

CBSE 12th Term-2 2022 : Physics Solve Short Questions For Final Revision Before Exam

 

Check out some of the CBSE Class 12 Physics questions listed below with solutions which are important for CBSE Term 2 Exam 2022. The questions will be useful for the students appearing for Physics Term 2 Exam 2022 on May 20, 2022. Read the following questions and score well:

CBSE Class 12 Term 2 Study Material
CBSE Class 12 Reduced Syllabus for Term 2 Exam 2022	CBSE Class 12 Sample Paper for Term 2 Exam 2022
CBSE Class 12 Previous Year Question Paper with Solutions	CBSE Class 12 Term 2 Full Study Material 2022
CBSE Revision Notes For Class 12	CBSE Class 12 Topper Answer Sheet

CBSE Class 12 Physics: Short Questions 

Que 1. Name the part of the electromagnetic spectrum of wavelength 10-2 m and mention its one application.

Ans : Microwave is the part of the electromagnetic spectrum of wavelength 10−2m

Application : Used in RADAR system for aircraft navigation.

Que 2. Write the following radiations in ascending order in respect of their frequencies; X-rays, Microwaves, UV rays and radiowaves.

Ans : Referring to the electromagnetic spectrum shown in the figure, the radiations in an ascending order of frequencies are :

1. Radio Waves
2. Microwaves
3. Ultra Violet Rays
4. X rays

Que 3. Name the part of electromagnetic spectrum which is suitable for : 

(i) radar systems used in aircraft navigation 

(ii) treatment of cancer tumours.

Ans : (i) Microwave (ii) γ -rays.

Que 4. Name the EM waves used for studying the crystal structure of solids. What is its frequency range?

Ans : X-Rays. Frequency range : 3 x 10¹⁶ Hz ^{– 3} x 10¹⁹ Hz.

Que 5. Which part of the electromagnetic spectrum has the largest penetrating power?

Ans : Gamma rays have maximum energy and hence, maximum penetration power.

Que 6. Which part of the electromagnetic spectrum is absorbed from sunlight by ozone layer?

Ans : Ultraviolet light is absorbed by the ozone layer.

Que 7. Which part of the electromagnetic spectrum is used in operating a RADAR?

Ans : Microwaves are used in operating a RADAR.

Que 8. Name the part of electromagnetic spectrum whose wavelength lies in the range of 10⁻¹⁰m Give its one use.

Ans : The X rays have a wavelength range as 10⁻⁸m − 10⁻¹²m . Therefore, the part of the electromagnetic spectrum which comes under the range of 10⁻¹⁰m  is X-ray. Use of X rays. X-rays have a smaller wavelength and higher energy. Therefore they are used to study crystal structure as they are useful to explore the structure of crystals.

Que 9. Which of the following has the shortest wavelength: Microwaves, Ultraviolet rays, X-rays.

Ans : X-rays has shortest wavelength.

Que 10. Arrange the following in descending order of wavelength: X-rays, Radio waves, Blue light, Infrared light

Ans : Radiowaves, Infrared light, Blue light, X-rays.

Que 11. A convex lens is placed in contact with a plane mirror. A point object at a distance of 20 cm on the axis of this combination has its image coinciding with itself. What is the focal length of the lens?

Ans : 

Figure shows a convex lens placed in contact with a plane mirror. An axial point object is placed at a distance O at a distance, OC = 20cm. As the image I of the object coincides with O, the rays refracted first from the lens and then refracted by the plane mirror must be retracing their path. This would happen when rays refracted by the convex lens fall normally on the mirror I.e, the refracted rays form a beam parallel to principal axis of the lens. Hence the object O must be at the focus of the convex lens. f = CO = 20 cm.

Que 12. For the same value of angle of incidence, the angles of refraction in three media A, B and C are 15°, 25° and 35° respectively. In which medium would the velocity of light be minimum?

Ans : As light travels from a rarer to denser medium it bends towards the normal as its speed decreases. So, if the bending is more, the speed of the light would be less in that medium, compared to other media. As the angle of refraction is measured with respect to the normal, the ray making the least angle of refraction would bend more and the speed of light would be minimum in that case. So, the correct option is medium A where refracting angle is 15°.

Que 13. When monochromatic light travels from one medium to another, its wavelength changes but frequency remains the same. Explain.

Ans : Frequency is the characteristic of the source while wavelength is the characteristic of the medium. when monochromatic light travels from one medium to another its speed changes so its wavelength  changes but frequency $v$ remains unchanged.

Que 14. State the criteria for the phenomenon of total internal reflection of light to take place.

Ans :

• Total internal reflection of light is the process in which the light ray completely reflected within a medium such as water or glass from the surrounding surfaces back into the medium.
• The condition for the total internal reflection area as follows :

1. The ray of light must travel from denser medium to rarer medium but not from rarer to denser.

2. The angle of incidence must be greater than critical angle. Critical angle is given by : 

Que 15. A concave lens of refractive index 1.5 is immersed in a medium of refractive index 1.65. What is the nature of the lens?

Ans: The lens behaves as convex.

When the refractive index of a surrounding medium is more than refractive index of material of concave lens then the nature of the lens changes.

Que 17. What is the shape of the wavefront diverging from a point source of light?

Ans : Point source has spherical wave front.

Que 18. What is the phase difference between any two points lying on the same?

Ans :Wave front is the locus of all the particles of a medium that are found vibrating in the same phase. The phase difference between any two points on a wavefront is zero.

Que 19. What is the shape of wavefront obtained from a point source at a (i) small distance (ii) large distance? 

Ans : (i) Spherical wavefront 

(ii) Plane wavefront. 

Que 20. Under what conditions a cylindrical wavefront is obtained? 

Ans : A cylindrical wavefront is obtained at a small distance from a linear source of light. 

Que 21. What type of wavefront is obtained when a plane wave is reflected by a concave mirror?

Ans : Spherical wavefront (converging). 

Que 22. Do all waves exhibit diffraction or only light? 

Ans : All the waves exhibit the phenomenon of diffraction. 

Que 23. What is the maximum intensity of light in Young’s double slit experiment if the intensity of light emerging from each slit is I_o? 

Ans : Maximum intensity of light in Young’s double slit experiment is 4I_o. 

Que 24. What are the two methods for obtaining coherent sources in the laboratory?

Ans : (1) Lloyd's mirror

(2) Fresnel's biprism

Que 25. How can electron be made to leave the metal surface?

Ans : If we want to remove the electron from the metal surface, we have to give some energy to the electron which would break the force of interaction between the nucleus and the electron so that it can leave the metal surface.

Que 26. The maximum kinetic energy of a photoelectron is 3eV. What is its stopping potential?

Ans : 

Que 27. How does the stopping potential applied to a photocell change, if the distance between the light source and the cathode of the cell is doubled?

Ans : Stopping potential remains unchanged. 

Reason: On doubling the distance between the light source and the cathode of the cell, the intensity of light incident on the photocell becomes one-fourth. As stopping potential does not depend on intensity, the stopping potential remains unchanged.

Que 28. On what factors the value of stopping potential depends ?

Ans : Stopping potential depends on frequency of incident light.

Que 29. A proton and an electron have same velocity. Which one has greater de-Broglie wavelength and why?

Ans : de Broglie wavelength (λ) is given as

λ = h/mv

Given v_p =v_e

where v_p = velocity of proton

v_e = velocity of electron

Since m_p > m_e

From the given relation

λ ∝1/m, hence λ_p < λ_e

Thus, electron has greater de Broglie wavelength, if accelerated with same speed.

Que 30. Define intensity of radiation on the basis of photon picture of light. Write its S.I. unit

Ans : The intensity of radiation can be defined as the energy associated with photons emitted from a unit surface area in unit time. Its S.I. unit is joule/metre²second or (J/m²s).

Que 31. The stopping potential in an experiment on photoelectric effect is 1.5V. What is the maximum kinetic energy of the photoelectrons emitted? Calculate in Joules.

Ans : We know that KE_max  = eV₀ 

V₀ = 1.5V  

= 1.6 × 10^-19 × 1.5 

= 2.4 × 10^-19 J

KE = 2.4  × 10^-19 J 

Que 32. If the wavelength of Electromagnetic radiation is doubled, what happens to the energy of photon?

Ans : 

∴ The energy of photon reduces to half of its initial value

Que 33. Define mass defect?

Ans : Mass defect: It is observed that the mass of a nucleus is smaller than the sum of the masses of the constituent nucleons in the free state. The difference between the actual mass of the nucleus and the sum of the masses of constituent nucleons is called mass defect.

The mass defect is

Δm = [Zm_p + (A - Z)m_n] - M

where,

Z is the atomic number (number of protons),

A is the mass number,

(A - Z) is the number of neutrons,

m_p is the mass of a proton,

m_n is the mass of a neutron and 

M is the measured mass of a nucleus.

Que 34. Name the series of hydrogen spectrum, which has least wavelength.

Ans : The Lyman series.

Que 35. Why is the classical (Rutherford) model for an atom of electron orbitting around the nucleus not able to explain the atomic Structure?

Ans : The classical method could not explain the atomic structure as the electron revolving around the nucleus are accelerated and emits energy as the result, the radius of the circular paths goes on decreasing. Ultimately electrons fall into the nucleus, which is not in practical.

Que 36. Write the expression for Bohr’s radius in hydrogen atom ?

Ans : 

Que 37. Two nuclei have mass numbers in the ratio 1: 2. What is the ratio of their nuclear densities?

Ans : Nuclear density is independent of mass number. Hence, both the atoms have the same nuclear density.

Que 38. Two nuclei have mass numbers iin the ratio 1 : 8. What is the ratio of their nuclear radii?

Ans : Nuclear radius, 

Que 39. Two nuclei have mass numbers in the ratio 8 : 125. What is the ratio of their nuclear radii?

Ans: Nuclear radius 

Que 40. What is the angular momentum of an electron in the third orbit of an atom?

Ans : Here n = 3; h = 6.6 x 10^-34 Js

Angular momentum

Que 41. Why did Rutherford select a gold foil in his $\alpha$-ray scattering experiment?

Ans : For the scattering experiment, Rutherford wanted a metal sheet which could be as thin as possible. Gold is the most malleable of all known metals. It can easily be converted into very thin sheets. Hence, Rutherford selected a gold foil for his alpha-ray scattering experiment.