PUC Science 2nd PUC Class 12 - Karnataka Board PUC Important Questions

A long straight wire of a circular cross-section of radius ‘a’ carries a steady current ‘I’. The current is uniformly distributed across the cross-section. Apply Ampere’s circuital law to calculate the magnetic field at a point ‘r’ in the region for (i) r < a and (ii) r > a.

State the underlying principle of working of a moving coil galvanometer. Write two reasons why a galvanometer can not be used as such to measure current in a given circuit. Name any two factors on which the current sensitivity of a galvanometer depends.

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

Derive the expression for force per unit length between two long straight parallel current carrying conductors. Hence define one ampere.

Explain the principle and working of a cyclotron with the help of a schematic diagram. Write the expression for cyclotron frequency.

Predict the polarity of the capacitor in the situation described below :

Why should the material used for making permanent magnets have high coercivity?

What is the direction of induced currents in metal rings 1 and 2 when current I in the wire is increasing steadily? 

Show diagrammatically how an alternating emf is generated by a loop of wire rotating in a magnetic field. Write the expression for the instantaneous value of the emf induced in the rotating loop.

Define self inductance. Write its S.I. units.

Derive an expression for self inductance of a long solenoid of length l, cross-sectional area A having N number of turns.

Why does current in a steady state not flow in a capacitor connected across a battery? However momentary current does flow during charging or discharging of the capacitor. Explain. 

A series LCR circuit is connected to a source having voltage v = v_m sin ωt. Derive the expression for the instantaneous current I and its phase relationship to the applied voltage.

Obtain the condition for resonance to occur. Define ‘power factor’. State the conditions under which it is (i) maximum and (ii) minimum.

 Derive an expression for the average power consumed in a series LCR circuit connected to a.c. source in which the phase difference between the voltage and the current in the circuit is Φ.

Describe briefly, with the help of labelled diagram, working of a step-up transformer.

A step-up transformer converts a low voltage into high voltage. Does it not violate the principle of conservation of energy? Explain.

You are given the following three lenses. Which two lenses will you use as an eyepiece and as an objective to construct a compound microscope?

Define resolving power of a microscope and write one factor on which it depends

Define the magnifying power of a compound microscope when the final image is formed at infinity. Why must both the objective and the eyepiece of a compound microscope has short focal lengths? Explain.

Why should the objective of a telescope have large focal length and large aperture? Justify your answer. 

When are two objects just resolved? Explain.