List of top Physics Questions asked in CBSE CLASS XII

A small telescope has an objective lens of focal length 144cm and an eyepiece of focal length 6.0cm. What is the magnifying power of the telescope?What is the separation between the objective and the eyepiece?

At room temperature (27.0 °C) the resistance of a heating element is 100 Ω. What is the temperature of the element if the resistance is found to be 117 Ω, given that the temperature coefficient of the material of the resistor is \(1.70 \times 10^{-4} °C^{-1}.\)

A person with a normal near point(25cm)using a compound microscope with an objective of focal length 8.0mm and an eyepiece of focal length 2.5cm can bring an object placed at 9.0mm from the objective in sharp focus. What is the separation between the two lenses? Calculate the magnifying power of the microscope.

A compound microscope consists of an objective lens of focal length 2.0cm and an eyepiece of focal length 6.25cm separated by a distance of 15cm. How far from the objective should an object be placed in order to obtain the final image at(a)the least distance of distinct vision (25cm), and(b)at infinity? What is the magnifying power of the microscope in each case?

A long straight wire carries a current of 35 A. What is the magnitude of the field B at a point 20 cm from the wire?

A horizontal overhead power line carries a current of 90 A in east to west direction. What is the magnitude and direction of the magnetic field due to the current 1.5 m below the line?

A long straight wire in the horizontal plane carries a current of 50 A in north to south direction. Give the magnitude and direction of B at a point 2.5 m east of the wire.

A battery of emf 10 V and internal resistance 3 Ω is connected to a resistor. If the current in the circuit is 0.5 A, what is the resistance of the resistor? What is the terminal voltage of the battery when the circuit is closed?

The storage battery of a car has an emf of 12 V. If the internal resistance of the battery is 0.4Ω, what is the maximum current that can be drawn from the battery?

What is the de Broglie wavelength of
(a) a bullet of mass 0.040 kg travelling at the speed of 1.0 km/s,
(b) a ball of mass 0.060 kg moving at a speed of 1.0 m/s, and
(c)a dust particle of mass \(1.0×10^{–9}kg\) drifting with a speed of 2.2 m/s?
Light of frequency \(7.21×10^{14}Hz\) is incident on a metal surface. Electrons with a maximum speed of \(6.0×10^5 m/s\) are ejected from the surface.What is the threshold frequency for photoemission of electrons?
The work function for a certain metal is 4.2 eV. Will this metal give photoelectric emission for incident radiation of wavelength 330 nm?

Double-convex lenses are to be manufactured from a glass of refractive index 1.55, with both faces of the same radius of curvature. What is the radius of curvature required if the focal length is to be 20 cm?

A beam of light converges at a point P. Now a lens is placed in the path of the convergent beam 12cm from P. At what point does the beam converge if the lens is(a)a convex lens of focal length 20cm, and(b)a concave lens of focal length 16cm?

What is the focal length of a convex lens of a focal length of 30cm in contact with a concave lens of a focal length of 20cm? Is the system a converging or a diverging lens? Ignore the thickness of the lenses.

From the relation \(R = R_0A^{\frac{1}{3}}\), where \(R_0\) is a constant and A is the mass number of a nucleus, show that the nuclear matter density is nearly constant (i.e. independent of A).

The threshold frequency for a certain metal is \(3.3×10^{14} Hz\). If light of frequency \(8.2×10^{14} Hz\) is incident on the metal,predict the cut-off voltage for the photoelectric emission.
In an experiment on photoelectric effect,the slope of the cut-off voltage versus frequency of incident light is found to be \(4.12×10^{–15} V s\). Calculate the value of Planck’s constant.
Calculate the height of the potential barrier for a head on collision of two deuterons.(HINT:The height of the potential barrier is given by the Coulomb repulsion between the two deuterons when they just touch each other. Assume that they can be taken as hard spheres of radius 2.0 fm.)
Monochromatic light of wavelength 632.8 nm is produced by a helium-neon laser.The power emitted is 9.42 mW.
(a) Find the energy and momentum of each photon in the light beam,
(b)How many photons per second, on the average, arrive at a target irradiated by this beam? ( Assume the beam to have uniform cross-section which is less than the target area ), and
(c)How fast does a hydrogen atom have to travel in order to have the same momentum as that of the photon?
Find the
(a)maximum frequency, and
(b)minimum wavelength of X-rays produced by 30 kV electrons
 

How long can an electric lamp of 100W be kept glowing by fusion of 2.0 kg of deuterium? Take the fusion reaction as
\(^{2}_{1}H + ^{2}_{1}H →^{3}_{1}He + n + 3.27 \space MeV\)

The fission properties of \( ^{239}_{ 94} Pu\) are very similar to those of \(^{235}_{92} U\). The average energy released per fission is 180 MeV. How much energy, in MeV, is released if all the atoms in 1 kg of pure. \( ^{239}_{ 94} Pu\) undergo fission?

Suppose we think of fission of a \(^{56}_{26}Fe\) nucleus into two equal fragments, \(^{28}_{13} Al.\) Is the fission energetically possible? Argue by working out Q of the process. Given \(m\)(\(^{56}_{26}Fe\)) = 55.93494 u and \(m\)(\(^{28}_{13} Al\)) = 27.98191 u.

The Q value of a nuclear reaction A + b → C + d is defined by
Q = [mA+mb–mC–md]c2 
where the masses refer to the respective nuclei. Determine from the given data the Q-value of the following reactions and state whether the reactions are exothermic or endothermic.
(i) \(^{1}_{ 1} H + ^{3} _{1}H → ^{2}_{1} H + ^{2}_{1} H\)
(ii) \(^{12}_{6} C + ^{12}_{6} C → ^{12}_{10} Ne + ^{4}_{2} He\)
Atomic masses are given to be
\(m (^{2}_{ 1} H)\) = 2.014102 u
\(m (^{3}_{1} H) \)= 3.016049 u
\(m (^{12}_{ 6} C) \)= 12.000000 u
\(m (^{20}_{10} Ne)\) = 19.992439 u