MODEL PAPER 7 Physics - MODEL PAPER 7

A microscope is focused on a mark. Then a glass slab of refractive index 1.5 and thickness 6 cm is placed on the mark. To get the mark again in focus the microscope should be moved

Consider the two idealised systems: (i) a parallel plate capacitor with large plates and small separation and (ii) a long solenoid of length L > > R, radius of cross-section. In (i), E is ideally treated as a constant between plates and zero outside. In (ii), magnetic field is constant inside the solenoid and zero outside. These idealised assumptions, however, contradict fundamental laws as below:

In a compound microscope, maximum magnification is obtained when the final image

Two bulbs each marked 100 W, 220 V are connected in series across 220 V supply. The power consumed by them, when lit, is

Assertion (A): Two adjacent conductors of unequal dimensions, carrying the same positive charge have a potential difference between them.
Reason (R): The potential of a conductor depends upon the charge given to it.

Distinguish between diamagnetic and ferromagnetic materials in terms of
i. susceptibility and
ii. their behaviour in a non-uniform magnetic field

A proton and an alpha particle having the same kinetic energy are, in turn, passed through a region of the uniform magnetic field, acting normal to the plane of the paper and travel in circular paths. Deduce the ratio of the radii of the circular paths described by them.

Figure shows a rectangular conducting loop PQRS in which arm RS of length I is movable. The loop is kept in a uniform magnetic field B directed downward perpendicular to the plane of the loop. The arm RS is moved with a uniform speed v.


Deduce an expression for
i. the emf induced across the arm RS
ii. the external force required to move the arm and
iii. the power dissipated as heat.

A homogeneous poorly conducting medium of resistivity fills up the space between two thin coaxial ideally conducting cylinders. The radii of the cylinders are equal to a and b with a < b, the length of each cylinder is l. Neglecting the edge effects, find the resistance of the medium between the cylinders.

Define the term self-inductance of a solenoid. Obtain the expression for the magnetic energy stored in an inductor of self-inductance L to build up a current I through it.

Define the term wavefront. State Huygen's principle. Consider a plane wavefront incident on a thin convex lens. Draw a proper diagram to show how the incident wavefront traverses through the lens and after refraction focusses on the focal point of the lens, giving the shape of the emergent wavefront.

i. With the help of a diagram, explain the principle and working of a device which produces current that reverses its direction after regular intervals of time.
ii. If a charged capacitor C is short-circuited through an inductor L, the charge and current in the circuit oscillate simple harmonically. a. In what form the capacitor and the inductor store energy? b. Write two reasons due to which the oscillations become damped.

Derive an expression for potential due to a dipole for distances large compared to the size of the dipole. How is the potential due to dipole different from that due to a single charge?