CBSE practice Questions

# 12 CBSE Sample Paper Physics [PDF]

This 12 CBSE Sample Paper for Physics consists 30 questions according to 12 CBSE Board Physics exam pattern. You can download complete sample paper in PDF using link below last question

### 1 MARK QUESTIONS

Question: Write two energy losses in a Transformer.

Question: Will an induced current develop in the conductor moved in direction parallel to magnetic field?

Question: The instantaneous value of voltage from an a.c. Source is given by E = 300 Sin 314t. What is the r.m.s. voltage of the source?

Question: An alpha particle enters a region of electric and magnetic field and passes without deviation in its path. What is the net force acting on the particle in the region?

Question: Draw an equipotential surface in a uniform electric field.

Question: How a wavelength of light is associated with the stopping potential. Draw a graph between them.

Question: Why do magnetic lines of force prefer to pass through iron than through air?

Question: The colour bands of a carbon resistor are in sequence yellow, blue, green and silver respectively. Compute the value of its resistance.

Question: Suppose that the lower half of a concave mirror’s reflecting surface is covered with an opaque non-reflecting material. What effect this have on the image of an object placed in front of the mirror?

Question: What is gamma decay? Give an example.

Question: Define electric susceptibility. How its related to dielectric constant?

Question: The debroglie wavelengths associated with a proton and a neutron, are found to be equal which of the two has a higher value for kinetic energy?

Question: An electron moving through a magnetic field does not experiences a force. Under what condition is this possible?

Question: What is the Brewster angle for air to glass transition? (Refractive index of glass = 1.5)

Question: Zener diode has higher dopant densities as compared to ordinary p-n junction diodes. How does it affect (i) width of the depletion layer? (ii) Junction field?

Question: A carbon resistor is marked with yellow violet and red colour strips. What is its resistance?

Question: Name two optoelectronic devices .Write on use of each.

Question: Why is the transmission of signals using ground waves restricted to frequencies upto 1500KHz?

Question: The electric potential V is constant in a given region. What is the value of electric field there?

Question: The electric field between two parallel plates of capacitor changes with time, a current begins to flow in between the plates. Write the related law.

Question: Draw a spherical wave front by a point source of light.

Question: If a wire is stretched to double its original length without loss of mass, how will resistivity of the wire be influenced?

Question: Why is de-Broglie wave associated with a moving football not visible?

Question: A partially plane polarized beam of light is passed through Polaroid. Show graphically the variation of the transmitted light intensity and angle of rotation of the Polaroid.

Question: What is the angle between the directions of electric field at any (i) axial point and (ii) equatorial point due to an electric dipole?

Question: The polarizing angle of a medium is 60degrees.What is the refractive index of the medium?

Question: How does the presence of dielectric medium, in between the two charges, affect the electrostatic force between them?

Question: When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge.

Question: What is the power factor of an LCR series circuit at resonance?

Question: Can two p-n junction diodes placed back to back work as PnP transistor?

Question: An electron revolves around the nucleus in an atom. What is the work done on electron?

### 2 MARK QUESTIONS

Question: Two long and Parallel straight wires A and B carrying currents of 8.0 A and 5.0A in the same direction are separated by a distance of 4 cm. Estimate the force and direction on a 10 c.m. section of wire A.

Question: Can a body be at rest as well as in motion at same time. Explain, why?

Question: Name the physical quantity whose SI unit is curie (Ci): how is this quantity related to (a) disintegration constant (b) half life, and(c) mean life of the radioactive element?

Question: Estimate the distance for which ray optics is good approximation for an aperture of 4 mm and wave length 400 nm.

Question: What are heating waves? Name the radiations, which are next to these radiations in electromagnetic spectrum having longer wavelength.

Question: Why radio waves are communication waves .Write two uses of the waves.

Question: Draw a circuit diagram of potentiometer to find internal resistance of a cell and Establish formula for it.

Question: Show the variation of current versus voltage graph for GaAs and mark the (i) Non- linear region (ii) Negative resistance region.

Question: A light body and a heavy body both have equal kinetic energy. Which has higher momentum? And why?

Question: Write the function of (i) Transducer and (ii) Repeater in the context of communication system.

Question: State laws which are used for calculating equivalent resistance of unbalanced wheat stone bridge.

Question: A concave lens has the same radii of curvature for both sides and has a refractive index 1.6 in air. In the second case it is immersed inside a liquid of refractive index 1.4. Calculate the ratio of focal length of the lens in the two cases.

Question: The motion by a body is described by the equation, u = at. Find the distance travelled by the body in first 4 sec.

Question: Define current sensitivity and voltage sensitivity of a galvanometer. Increasing the current sensitivity may not necessarily increase the voltage sensitivity of a galvanometer. Justify.

Question: A charge q moving in a straight line is accelerated by a potential difference V.It enters a uniform magnetic field B perpendicular to its path. Deduce in terms of V an expression for the radius of the circular path in which it travels.

Question: Write short notes on DAVISSON and GERMER EXPERIMENT.

Question: How does the kinetic energy of an object vary on increasing its velocity by 10%.

Question: Define friction .Write its dimensional formula. Explain why (i) Ball bearings are used in machinery? (ii) We sometime slip on floor on a rainy day?

Question: Calculate the (i) momentum and (ii) de- broglie wavelength of the electron accelerated through the Potential difference of 56V.

Question: A constant force acting on a body of mass 3 kg changes its velocity from 2 m/s to 36 km/h in 6 seconds. Calculate the magnitude of the force and also write its direction.

Question: Define electric resistance .Write it’s SI unit. How does resistance of a conductor vary if (a) Conductor is stretched to 4 times of it’s length? (b) Temperature of conductor is increased? (c) You are given two wire of same length and thickness, one is of copper and other is of silver, which one has higher resistance?

Question: An electric heater is connected, turn by turn, to a D.C and A.C sources of equal voltages. Will the rate of heat production be same in the two cases? Explain

Question: The total energy of an electron in the first excited state of the Hydrogen atom is about -3.4 eV.(i) What is the kinetic energy of the electron in this state? (ii) What is the potential energy of the electron in this state?

Question: State Newton’s second law. Deduce Newton’s first law from it.

Question: A converging lens has a focal length 20cm in air. It is made of a material of refractive index 1.6 .It is immersed in a liquid of refractive index 1.3, what will be its new focal length? Draw the ray diagram.

Question: The work function of caesium is 2.14 eV. Find (a) the threshold frequency for caesium, and (b) the wavelength of the incident light if the photocurrent is brought to zero by a stopping potential of 0.60 V.

Question: A projectile has a range of 60 m and can reach a maximum height of 15 m. Calculate the angle at which projectile is fired?

Question: When 100 volts d.c is applied across an inductor, a current of 1A flows through it. If the same inductor is connected across 100 v a.c. source, a current reduces to 0.5 A. Why is the current reduced in later case? Calculate the reactance.

Question: A massage signal of 12 kHz and peak voltage 20 V is used to modulate a carrier wave of frequency 12 MHz and peak voltage 30V. Calculate the (i) modulation index (ii) Side –band frequencies.

Question: State Gauss Theorem and establish an expression for field due to a uniformly charged infinite plane sheet.

Question: Define electrical conductivity. How it is related to current density?

### 3 MARK QUESTIONS

Question: What do you mean by modulation, how it can be done, write its necessity.

Question: (a) ‘Friction is a necessary evil’. Give examples in support of your answer.
(b) Write in three methods to reduce friction.

Question: Which two main considerations are kept in amind while designing the objective lens of an astronomical telescope? Obtain an expression for the magnifying power of an astronomical telescope in its normal adjustment position.

Question: Define Digital logic gate. Draw the logic symbol of NAND gate. Write its truth table and Boolean expression.

Question: Derive the expression for the electric potential due to an electric dipole at any point. Justify that the electric potential remains zero at the equatorial line of the dipole.

Question: Draw a schematic sketch of a cyclotron. Explain briefly how it works and how it is used to accelerate the charged particles. (i) Show that time period of ions in a cyclotron is independent of both the speed and radius of circular path. (ii) What is resonance condition? How is it used to accelerate the charged particles?

Question: Plot the graph for binding energy per nucleon as a function of mass number. Write it main features.

Question: What is satellite wave propagation? Which tow communication methods make use of this mode of propagation? Derive the expression for the height of transmitting antenna.

Question: Define Transformer, how it help to step- up and step -down the applied voltage obtain expression for transformation ratio.

Question: Draw a circuit diagram of transistor as a device. Write its two applications.

Question: A parallel plate capacitor is charged by a battery. If the distance between the plates is decreased. How would (i) the capacitance, (ii) the electric field between the plates and (iii) the energy stored in the capacitor, be affected? Justify your answer.

Question: Define polarizing angle. Derive the relation connecting polarising angle and the refractive index of a medium.

Question: Give the principle of a Van- de Graff generator with the help of suitable diagram; describe its construction and working. How is the leakage of charge minimized from the generator?

Question: Obtain the expression for magnification for a compound microscope at normal adjustment condition.

Question: A message signal of frequency 10KHz and peak voltage of 10 volts is used to modulate a carrier of frequency 1MHz and  peak voltage of 20 volts. Determine (a) nodulation index (b) the side bands produced.

Question: Draw the expected shape of the graphs, showing the variation of the flux, with time, in both the cases. What is the cause of the difference in the shapes of the two graphs?

Question: The wavelength of the second line of the blamer series in the hydrogen spectrum is 4861A0 .Calculate the wavelength of the first line.

Question: (a) A train 100 m long is moving with a velocity of 60 km/h. In what time shall it cross a bridge 1 km long? (b) A train goes from station A to B with a speed of 60 km/h and returns back with speed of 40 km/h. Calculate the average speed of the train.

Question: Derive an expression for the equivalent emf and internal resistance of a parallel combination of 2 primary cells. Under what condition is the potential difference across a cell equal to its emf?

Question: (a) Vijay was going to his college by a bus full of passengers, but he got sit, mean while at the next station an old lady entered the bus, he immediately stood up and offered the seat to the old lady. Write any four values showed by Vijay in this incidence. (b) Vijay (the boy in above question) knew few concepts of physics. Write any two.

### 5 MARK QUESTIONS

Question: Derive a relation between object and image distance when refraction of light takes place at a convex refracting surface. Mention the assumptions used. Using this result, derive the lens maker formula.

Question: What is an oscillator circuit? How a transistor as an oscillator works.

Question: What are coherent sources of light? State two conditions for two light sources to be coherent.
Derive a mathematical expression for the width of interference fringes obtained in Young’s double slit experiment with the help of a suitable diagram.

Question: State the essential condition for the diffraction of light to take place. A parallel beam of monochromatic light falls normally on a narrow slit and light coming out of the slit is obtained on the screen. Derive the expression for the conditions of secondary maxima and minima.
When a tiny circular obstacle is placed in the path of light from a distant source, a bright spot is seen at the centre of the shadow of the obstacle. Explain why?

Question: State the Biot-savart law for the magnetic field due to a current carrying element. Using this law obtain a formula for magnetic field at the centre of circular loop of radius R carrying a  steady current I.

Question: Define angular velocity and angular acceleration. Derive an expression for centripetal acceleration in case of uniform circular motion of an object.

Question: Draw a neat and labelled diagram of a cyclotron. State the underlying principle and explain how a positively charged particle gets accelerated in this machine show mathematically that the cyclotron frequency does not depend upon the speed of the particle.

Question: Show that the total mechanical energy of a body falling freely under gravity is conserved.

Question: Derive an expression for potential at a point due to electric dipole. Hence deduce values for potential at a point on: (a) Dipole Axis (b) Equatorial Plane.

Question: Draw a neat and labelled diagram of a cyclotron. State the underlying principle and explain how a positively charged particle gets accelerated in a cyclotron. Show mathematically that the cyclotron frequency does not depend on speed of the particle.

Question: (i) Derive the mirror formula which gives the relation between f, v and u. Write the corresponding formula for a thin lens?
(ii) A Screen is placed 90 cm from an object. The image of the object on the screen is formed by a convex lens at two different locations separated by 20 cm. Determine the focal length of the lens.

Question: Explain the working of n-p-n transistor as common emitter amplifier. What is phase difference between input signal and output signal? State any two reason why a common emitter amplifier is preffered to a common base amplifier?

Question: How a full wave rectifier works. Draw its Diagram. Write the function of filter circuits.

Question: Explain the function of base region of a transistor. Why is this region made thin and lightly doped?
Draw a circuit diagram to study the input and output characteristics of n-p-n transistor in a common emitter (CE) configuration.
Show these characteristics graphically. Explain how current amplification factor of the transistor is calculated using output characteristics.

Question: Find the expression for the capacitance of a parallel plate capacitor of area A and plate separation d (a) a dielectric slab of thickness t, and (b) a metallic slab of thickness t, where t < d are introduced  one by one between the plates of the capacitor. In which case would the capacitance be more and why?

Question: What is fringe width? Derive the expression a beam of light consisting of two wavelengths, 650 nm and 520 nm, is used to obtain interference fringes in a Young’s double-slit experiment. (a) Find the distance of the fourth dark fringe on the screen from the central maximum for wavelength 650 nm. (b) What is the least distance from the central maximum where the bright fringes due to both the wavelengths coincide? Given d=2 mm and D=120 cm.

Question: (a) Define electric flux. Write its S.I. unit.
(b) Using Gauss’s law, prove that the electric field at a point due to a uniformly charged infinite plane sheet is independent of the distance from it.
(c) How field is directed if (I) the sheet is positively charged, (II) negatively charged?

Question: What are energy bands? How are these formed? Distinguish between a conductor, an insulator and a semiconductor on the basis of energy band diagram. 