CBSE Class 12 Physics Solved Question Paper 2013

The charge on an unknown capacitor is given by,

Q = CV

On reducing the potential by 120 V, charge on the capacitor is reduced which is given by,

Q’ = C(V-120)

C(V-120) = 120 C                          … (2)

On solving equation (1) and (2), we have

 

Unknown capacitance from equation (1),

Q = CV

 

ii) Charge on the capacitor, if voltage is increased by 120V

Q = C (V+120)

   = 2 (180+120)

   = 600 C

                                                          OR




i) Electric flux through a surface, 
Flux through the left surface, 

Since x = 1m,

   

ii) Using Gauss Theorem, we can calculate the charge inside the cylinder.

V= E – I r;

The emf of a cell is greater than terminal voltage because there is some potential drop across the cell due to its small internal resistance.

Since the cells are in opposition,

E _net = E1 – E₂ = (200-10) = 190 V

So, current in the circuit is given by, I = 

Given, Resistance, R = 0.80

Maximum current, I_max = 1 A

So, Voltage across ammeter, V = IR = 1.0 0.80 = 0.8 V

i) If a shunt is connected in parallel,

Current I flowing through S is (I – I₁)

For parallel combination of resistors, 

I₁. R_A = ((I – I₁) S

 

This is the required value of shunt resistance. 

ii) Combined resistance of the ammeter and the shunt, 

When capacitor is charged by a dc source, 

Conduction current is equal to the displacement current.

i.e.,                           
Because,  is maximum when, capacitor is fully charged.

Given, a convex lens placed coaxially in contact with a concave lens. 

Power of convex lens, P₁ = 
Power of concave lens, P₂ = 

So, Power of combination, P = P₁ + P<sub>2 

                                                       =</sub>  
                                                      
Since, power has negative magnitude; system of lenses is diverging in nature.

The polarity of the induced emf at the open ends of a closed loop is such that it tends to produce a current which opposes the change in magnetic flux that produced it.



Emf will be induced at the ends. Magnetic flux changes in a metallic rod falling freely under gravity and hence, emf is induced.

Substances that can retain their magnetism for a long duration of time at room temperature are called permanent magnets. They have high retentivity and coercivity.

Eg: Steel, cobalt 

The equipotential surface for an isolated charge is concentric circles. The distance between the shell decreases with increase in electric field.