ISC (Science) ISC Class 12 - CISCE Important Questions for Physics (Theory)

A 60 Ω resistor, a 1.0 H inductor and a 4 μF capacitor are connected in series to an ac supply generating an emf e = 300 sin (500t) V. Calculate:

1. impedance of the circuit.
2. peak value of the current flowing through the circuit.
3. phase difference between the current and the supply voltage.

An ac generator generates an emf which is given by e = 311 sin (240 πt) V. Calculate:

1. frequency of the emf.
2. r.m.s. value of the emf.

A meter bridge is balanced with a known resistance (R) in the left hand gap and an unknown resistance (S) in the right hand gap. Balance point is found to be at a distance of 1 cm from the left hand side. When the battery and the galvanometer are interchanged, balance point will ______.

Three identical cells each of emf 'e' are connected in parallel to form a battery. What is the emf of the battery?

Three bulbs B₁ (230V, 40W), B₂ (230V, 60W) and B₃ (230V, 100W) are connected in series to a 230V supply. Which bulb glows the brightest?

The figure below shows two batteries, E1 and E2, having emfs of 18V and 10V and internal resistances of 1 Ω and 2 Ω, respectively. W₁, W₂ and W₃ are uniform metallic wires AC, FD and BE having resistances of 8 Ω, 6 Ω and 10 Ω respectively. B and E are midpoints of the wires W₁ and W₂. Using Kirchhoff's laws of electrical circuits, calculate the current flowing in the wire W₃:

The Figure below shows a potentiometer circuit in which the driver cell D has an emf of 6 V and internal resistance of 2 Ω. The potentiometer wire AB is 10 m long and has a resistance of 28 Ω. The series resistance R_S is of 2 Ω.

1. The current I_p flowing in the potentiometer wire AB when the jockey (J) does not touch the wire AB.
2. emf of the cell X if the balancing length AC is 4.5 m.

Current I flowing through a metallic wire is gradually increased. Show graphically how heating power (P) developed in it varies with the current (I).

In a potentiometer, a cell is balanced against 110 cm when the circuit is open. A cell is balanced at 100 cm when short-circuited through a resistance of 10 Ω. Find the internal resistance of the cell.

Study the two circuits shown in the figure below. The cells in the two circuits are identical to each other. The resistance of the load resistor R is the same in both circuits.

If the same current flows through the resistor R in both circuits, calculate the internal resistance of each cell in terms of the resistance of resistor R. Show your calculations.

The drift velocity of electrons in a conductor connected to a battery is given by v_d = `(−"eE" τ)/"m"`. Here, e is the charge of the electron, E is the electric field, τ is the average time between collisions and m is the mass of the electron.

Based on this, answer the following:

1. How does the drift velocity change with a change in the potential difference across the conductor?
2. A copper wire of length 'l' is connected to a source. If the copper wire is replaced by another copper wire of the same area of cross-section but of length '4l', how will the drift velocity change? Explain your answer.

A circular coil carrying a current I has radius R and number of turns N. If all the three, i.e. the current
I, radius R and number of turns N are doubled, then, the magnetic field at its centre becomes:

(a) Double

(b) Half

(c) Four times

(d) One fourth

How will you convert a moving coil galvanometer into a voltmeter?

A moving charged particle q travelling along the positive x-axis enters a uniform magnetic field B.
When will the force acting on q be maximum?

A long horizontal wire P carries a current of 50A. It is rigidly fixed. Another wire Q is placed directly above and parallel to P, as shown in Figure 1 below. The weight per unit length of the wire Q is 0.025 Nm-1 and it carries a current of 25A. Find the distance 'r' of the wire Q from the wire P so that the wire Q remains at rest

Explain the term hysteresis

Obtain an expression for magnetic flux density B at the centre of a circular coil of radius R, having N turns and carrying a current I

Why are the pole pieces of a horseshoe magnet in a moving coil galvanometer made cylinder in shape? 

An electric current I flows through an infinitely long conductor as shown in Figure 2 (a) below. Write an expression and direction for the magnetic field at point P. 

An electric current I flows through a circular loop as shown in Figure 2(b) below. Write an expression and direction for the magnetic field at the centre of the loop at point P.