List of top Physics Questions asked in CBSE CLASS XII

A point charge of \(2.0\,µC\) is at the centre of a cubic Gaussian surface 9.0 cm on edge. What is the net electric flux through the surface?
A uniformly charged conducting sphere of \( 2.4\,m\) diameter has a surface charge density of \(80.0\,µCm^{-2}\) . 
(a) Find the charge on the sphere. 
(b) What is the total electric flux leaving the surface of the sphere?
A point charge causes an electric flux of \(−1.0 × 10^3 Nm^2 C^{-1}\) to pass through a spherical Gaussian surface of 10.0 cm radius centered on the charge. 
(a) If the radius of the Gaussian surface were doubled, how much flux would pass through the surface? 
(b) What is the value of the point charge?
A 12pF capacitor is connected to a 50V battery. How much electrostatic energy is stored in the capacitor?

Explain what would happen if in the capacitor given in Exercise 2.8, a 3 mm thick mica sheet (of dielectric constant = 6) were inserted between the plates,

(a) while the voltage supply remained connected.

(b) after the supply was disconnected.

(a)and(b)show the refraction of a ray in air incident at 60° with the normal to a glass-air and water-air interface, respectively. Predict the angle of refraction in glass when the angle of incidence in water is 45° with the normal to a water-glass interface
 

Three capacitors of capacitances 2 pF, 3 pF and 4 pF are connected in parallel. 

(a) What is the total capacitance of the combination? 

(b) Determine the charge on each capacitor if the combination is connected to a 100 V supply.

A point charge \(+10 µC\) is a distance 5 cm directly above the centre of a square of side 10 cm, as shown in Fig. 1.34. What is the magnitude of the electric flux through the square? (Hint: Think of the square as one face of a cube with edge 10 cm.)
 

Two charges 2 μC and –2 μC are placed at points A and B 6 cm apart.

(a) Identify an equipotential surface of the system.

(b) What is the direction of the electric field at every point on this surface?

A 4.5cm needle is placed 12cm away from a convex mirror of focal length 15cm. Give the location of the image and the magnification.Describe what happens as the needle is moved farther from the mirror.

A regular hexagon of side 10 cm has a charge 5 μC at each of its vertices. Calculate the potential at the centre of the hexagon.
Careful measurement of the electric field at the surface of a black box indicates that the net outward flux through the surface of the box is \(8.0 × 10^3 N m^2 C^{-1}. \)
(a) What is the net charge inside the box? 
(b) If the net outward flux through the surface of the box were zero, could you conclude that there were no charges inside the box? Why or Why not?

A small candle,2.5cm in size is placed at 27cm in front of a concave mirror of radius of curvature 36cm.At what distance from the mirror should a screen be placed in order to obtain a sharp image? Describe the nature and size of the image.If the  is moved closer to the mirror, how would the screen have to be moved?

Consider a uniform electric field \(E = 3 × 10^3 \,\hat{i} NC^{-1}\). 
(a) What is the flux of this field through a square of 10 cm on a side whose plane is parallel to the yz - plane? 
(b) What is the flux through the same square if the normal to its plane makes a \( 60^0\) angle with the x-axis?
A conducting sphere of radius 10 cm has an unknown charge. If the electric field 20 cm from the centre of the sphere is \(1.5 × 10^3 NC^{-1}\) and points radially inward, what is the net charge on the sphere?
What is the net flux of the uniform electric field of Exercise 1.15 through a cube of side 20 cm oriented so that its faces are parallel to the coordinate planes?
(a) Two insulated charged copper spheres A and B have their centers separated by a distance of 50 cm. What is the mutual force of electrostatic repulsion if the charge on each is \(6.5 × 10^{−7} C\)? The radii of A and B are negligible compared to the distance of separation. 
(b) What is the force of repulsion if each sphere is charged double the above amount, and the distance between them is halved?
A polythene piece rubbed with wool is found to have a negative charge of \(3 × 10^{−7} C\). 
(a) Estimate the number of electrons transferred (from which to which?) 
(b) Is there a transfer of mass from wool to polythene?
A system has two charge s \(q_A = 2.5 × 10^{−7} C\) and \(q_B = −2.5 × 10^{−7 }C\) located at points A: (0, 0, − 15 cm) and B: (0, 0, + 15 cm), respectively. What are the total charge and electric dipole moment of the system?
When a glass rod is rubbed with a silk cloth, charges appear on both. A similar phenomenon is observed with many other pairs of bodies. Explain how this observation is consistent with the law of conservation of charge.
The electrostatic force on a small sphere of charge 0.4 µC due to another small sphere of charge − 0.8 µC in air is 0.2 N.
(a) What is the distance between the two spheres?
(b) What is the force on the second sphere due to the first?