PUC Science 2nd PUC Class 12 - Karnataka Board PUC Question Bank Solutions for Physics

Consider the situation shown in the figure. Suppose the circular loop lies in a vertical plane. The rod has a mass m. The rod and the loop have negligible resistances but the wire connecting O and C has a resistance R. The rod is made to rotate with a uniform angular velocity ω in the clockwise direction by applying a force at the midpoint of OA in a direction perpendicular to it. Find the magnitude of this force when the rod makes an angle θ with the vertical.

Write the expression, in a vector form, for the Lorentz magnetic force \[\vec{F}\] due to a charge moving with velocity \[\vec{V}\] in a magnetic field \[\vec{B}\]. What is the direction of the magnetic force? 

Write the principle of working of a metre bridge

In a metre bridge, the balance point is found at a distance l₁ with resistances R and S as shown in the figure.An unknown resistance X is now connected in parallel to the resistance S and the balance point is found at a distance l₂. Obtain a formula for X in terms of l₁, l₂ and S. 

State its any ‘two’ uses of photodiode.

Write the expression for the force `vecF` acting on a particle of mass m and charge q moving with velocity `vecV` in a magnetic field `vecB` , Under what conditions will it move in (i) a circular path and (ii) a helical path?

Show that the kinetic energy of the particle moving in a magnetic field remains constant.

In a meter bridge, the null point is found at a distance of l₁ cm from A. If now a resistance of X is connected in parallel with S, the null point occurs at l₂ cm. Obtain a formula for X in terms of l₁, l₂ and S.

Explain the formation of depletion layer and potential barrier in a p−n junction.

The figure shows experimental set up of a meter bridge. When the two unknown resistances X and Y are inserted, the null point D is obtained 40 cm from the end A. When a resistance of 10 Ω is connected in series with X, the null point shifts by 10 cm. Find the position of the null point when the 10 Ω resistance is instead connected in series with resistance ‘Y’. Determine the values of the resistances X and Y.

Light of wavelength 560 nm goes through a pinhole of diameter 0.20 mm and  falls on a wall at a distance of 2.00 m. What will be the radius of the central bright spot formed on the wall?

A convex lens of diameter 8.0 cm is used to focus a parallel beam of light of wavelength 620 nm. If the light is focused at a distance of 20 cm from the lens, what would be the radius of the central bright spot formed?

The dielectric constant decreases if the temperature is increased. Explain this in terms of polarization of the material.

When a dielectric slab is gradually inserted between the plates of an isolated parallel-plate capacitor, the energy of the system decreases. What can you conclude about the force on the slab exerted by the electric field?

A dielectric slab is inserted between the plates of an isolated capacitor. The force between the plates will

Assume that the magnetic field is uniform in a cubical region and zero outside. Can you project a charged particle from outside into the field, so that the particle describes a complete circle in the field?

A positively-charged particle projected towards east is deflected towards north by a magnetic field. The field may be

A charged particle is whirled in a horizontal circle on a frictionless table by attaching it to a string fixed at one point. If a magnetic field is switched on in the vertical direction, the tension in the string

A beam consisting of protons and electrons moving at the same speed goes through a thin region in which there is a magnetic field perpendicular to the beam. The protons and the electrons

A charged particle moves in a uniform magnetic field. The velocity of the particle at some instant makes an acute angle with the magnetic field. The path of the particle will be