# CBSE Class 12 Physics board exam 2018: Important 1 mark questions

Mayank Uttam

Important questions for CBSE Class 12 Physics board exam 2018 are available here. These are very short answer types questions (or 1 mark) questions.

According to the latest CBSE Class 12 Physics examination pattern, students will get 5 very short answer type questions in the section – A of the paper. Students need to answer 1 mark questions in one line or one word (according to the requirement of the question).

CBSE Examination Pattern or Blue Print: Class 12 Maths Board Exam 2018

These questions are basically conceptual questions and need the basic understanding of the concepts. Some memory based questions are also present.

Students preparing for Class 12 Physics board exam 2018 are advised to prepare these questions well. They are also advised to take print out of this page and answer these question with a pencil. In this way, they can easily learn the answers of these important questions for a very long time.

We have intentionally left the solutions of these questions because mugging up solutions of these questions is not the best way to prepare. Please note that two or more 1 mark questions can be clubbed and might be asked in 2 or 3 marks’ questions.

Important questions (1 mark) for Class 12 board exam 2018 are given below:

Question: In which orientation, a dipole placed in a uniform electric fields is in (i) stable, (ii) unstable equilibrium?

Question: A capacitor has been charged by a dc source. What are the magnitudes of conduction and displacement currents, when it is fully charged?

CBSE Class 12 Physics Sample Paper: 2018

Question: The emf of a cell always greater than its terminal voltage. Why? Give reason.

Question: Why do the equipotential due to a uniform electric field not intersect each other?

Question: Why is the potential inside a hollow spherical charged conductor constant and has the same value as on its surface?

Question: A charge ‘q’ is placed at the centre of a cube. What is the electric flux passing through the cube?

Question: Two wires of equal length, one of copper and the other of manganin have the same resistance. Which wire is thicker?

Question: Why is electrostatic potential constant throughout the volume of the conductor and has the same value (as inside) on its surface?

Question: Why must electrostatic field be normal to the surface at every point of a charged conductor?

Question: Why should electrostatic field be zero inside a conductor?

Question: Two insulated charged copper spheres A and B of identical size have charges qA and ‒3qA respectively. When they are brought in contact with each other and then separated, what are the new charges on them?

Question: What is the geometrical shape of equipotential surfaces due to a single isolated charge?

Question: Two insulated charged copper spheres A and B of identical size have charges qA and qB respectively. When they are brought in contact with each other and finally separated, what are the new charges on them?

Question: A hollow metal sphere of radius 5 cm is charged such that the potential on its surface is 10 V. What is the potential at the centre of the sphere?

Question: Define dipole moment of an electric dipole. Is it a scalar or a vector?

Question: A resistance R is connected across a cell of emf e and internal resistance r. A potentiometer now measures the potential difference between the terminals of the cell as V. Write the expression for ‘r’ in terms of e, V and R.

Question: Draw an equipotential surface for a system, consisting of two charges Q, ‒Q separated by a distance ‘r’ in air.

Question: What are permanent magnets? Give one example.

Question: A small magnet is pivoted to move freely in the magnetic meridian. At what place on the surface of the Earth will the magnet be vertical?

Question: A magnetic needle, free to rotate in a vertical plane, orients itself vertically at a certain place on the Earth. What are the values of (i) horizontal component of Earth’s magnetic field and (ii) angle of dip at this place?

Question: Name the electromagnetic waves, which (i) maintain the Earth’s warmth and (ii) are used in aircraft navigation.

Question: The susceptibility of a magnetic material is –4.2 × 10‒6. Name the type of magnetic materials it represents.

Question: The permeability of a magnetic material is 0.9983. Name the type of magnetic materials it represents.

Question: When current in a coil changes with time, how is the back emf induced in the coil related to it?

Question: Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid. Why?

Question: Define self-inductance. Give its S.I. units.

Question: Which of the following waves can be polarized (i) Heat waves (ii) Sound waves? Give reason to support your answer.

Question: Show on a graph the variation of the de Broglie wavelength (λ) associated with an electron, with the square root of accelerating potential (V).

Question: Write the relationship between the size of a nucleus and its mass number (A).

Question: The speed of an electromagnetic wave in a material medium is given by v = 1/(moεo)1/2

Question: What are the directions of electric and magnetic field vectors relative to each other and relative to the direction of propagation of electromagnetic waves?

Question: When electrons drift in a metal from lower to higher potential, does it mean that all the free electrons of the metal are moving in the same direction?

Question: Show on a graph, the variation of resistivity with temperature for a typical semiconductor.

Question: Show the variation of photocurrent with collector plate potential for different intensity but same frequency of incident radiation.

Question: Write two uses of X-rays.

Question: Show the variation of photocurrent with collector plate potential for different frequencies but same intensity of incident radiation.

Question: Write two uses of infrared rays.

Question: Define the term ‘threshold frequency’ in relations to photoelectric effects

Question: The peak value of emf in AC is E0. Write its (i) rms (ii) average value over a complete cycle.

Question: How is the mean life of a radioactive sample related to its half life?

Question: How are radio waves produced?

Question: Write any two characteristic properties of nuclear force.

Question: Define the term ‘stopping potential’ in relation to photoelectric effect.

Question: Define the term ‘wattless current’.

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

Question: Two nuclei have mass numbers in the ratio 1 : 8. What is the ratio of their nuclear radii?

Question: Identify the part of the electromagnetic spectrum to which the following wavelengths belong:

(i) 10‒1 m (ii) 10‒12 m

Question: What is sky wave propagation?

Question: Write the following radiations in ascending order in respect of their frequencies :

X-rays, microwaves, UV-rays and radio waves

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

Question:  Write the relationship between angle of incidence ‘i’, angle of prism ‘A’ and angle of minimum deviation for a triangular prism.

Question: Write the relation between de-Broglie wavelength (λ) associated with the electron and its kinetic energy E.

Question: What are isotopes? Give one example.

Question: How does focal length of a lens change when red light incident on it is replaced by violet light? Give reason for your answer.

Question: How does the fringe width, in Young’s double-slit experiment, change when the distance of separation between the slits and screen is doubled?

Question: Sketch the shape of wavefront emerging from a point source of light and also make the rays.

Question: Draw a diagram to show refraction of a plane wavefront incident on a convex lens and hence draw the refracted wave front.

Question: Unpolarized light is incident on a plane surface of refractive index m at angle i. If the reflected light gets totally polarized, write the relation between the angle i and refractive index m.

Question: What type of wavefront will emerge from a (i) point source, and (ii) distant light source?

Question: If the angle between the pass axis of polarizer and the analyser is 45°, write the ratio of the intensities of original light and the transmitted light after passing through the analyser.

Question: What is the geometrical shape of the wavefront when a plane wave passes through a convex lens?

Question: An object is held at the principal focus of a concave lens of focal length f. Where is the image formed?

Question: Two thin lenses of power +6 D and – 2 D are in contact. What is the focal length of the combination?

Question: How would the angular separation of interference fringes in Young’s double slit experiment change when the distance between the slits and screen is doubled?

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

Question: Under what condition does a biconvex lens of glass having a certain refractive index act as a plane glass sheet when immersed in a liquid?

Question: How does the angular separation between fringes in single-slit diffraction experiment change when the distance of separation between the slit and screen is doubled?

Question: A narrow beam of protons and deuterons, each having the same momentum, enters a region of uniform magnetic field directed perpendicular to their direction of momentum. What would be the ratio of the circular paths described by them?

Question: Write two uses of microwaves.

Question: Where on the surface of Earth is the angle of dip 90°?

Question: What happens to the width of depletion layer of a p-n junction when it is (i) forward biased, (ii) reverse biased?

Question: A plane electromagnetic wave travels in vacuum along y-direction. What can you say about the direction of electric and magnetic field vectors?

Question: A plane electromagnetic wave travels in vacuum along z-direction. What can you say about the direction of electric and magnetic field vectors?

Question: Show graphically, the variation of the de-Broglie wavelength (λ) with the potential (V) through which an electron is accelerated from rest.

Question: In a transistor, doping level in base is increased slightly. How will it affect (i) collector current and (ii) base current?

Question: An electron does not suffer any deflection while passing through a region of uniform magnetic field. What is the direction of the magnetic field?

Question: How does the width of the depletion layer of a p-n junction diode change with decrease in reverse bias?

Question: 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?

Question: You are given following three lenses. Which two lenses will you use as an eyepiece and as an objective to construct an astronomical telescope?

 Lenses Power (P) Aperture (A) L1 3 D 8 cm L2 6 D 1 cm L3 10 D 1 cm

Question: Which part of electromagnetic spectrum has largest penetrating power?

Question: Draw the logic circuit of NOT gate and write its truth table.

Question: What is the function of a Receiver in a communication system?

Question: What is the function of a transmitter in a communication system?

Question: Draw the logic circuit of AND gate and write its truth table.

Question: What is the function of 'Repeater' in communication system?

Question: Draw the logic circuit of NAND gate and write its truth table.

Question: Give the logic symbol of NOR gate.

Question: What is ground wave propagation?

These are some of the most important questions which are expected to be asked in CBSE Class 12 Physics board exam 2018. You can also get some important questions in solved papers. Links are given below

CBSE Class 12 Practice Papers

CBSE Class 12 Guess Papers

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