MODEL PAPER 1 Physics - MODEL PAPER 1

In the circuit given in the figure, an a.c. source of 200 V is connected through a diode D to a capacitor. The potential difference across the capacitor will be

An electron is travelling along the X-direction. It encounters a magnetic field in the Y-direction. Its subsequent motion will be:

The cations and anions are arranged in alternate form in

Assertion (A) :A step-up transformer cannot be used as a step-down transformer.
Reason (R): A transformer works only in one direction.

Assertion (A) : Light added to light can produce darkness.
Reason (B) : When two coherent light waves interfere, there is darkness at position of destructive interference.

Assertion : For a charged particle moving from point P to point Q, the net work done by an electrostatic field on the particle is independent of the path connecting point P to point Q.
Reason : The net work done by a conservative force on an object moving along a closed loop is zero.

Assertion (A): The photoelectrons produced by a monochromatic light beam incident on a metal surface, have a spread in their kinetic energies.
Reason (R): The work function of the metal varies as a function of depth from the surface

What information would you wish to know about the galvanometer before converting it into an ammeter or voltmeter?

Explain the formation of potential barrier and depletion region in a p-n junction diode. What is effect of applying forward bias on the width of depletion region?

A uniform magnetic field gets modified as shown below, when two specimens X and Y are placed in it.



i. Identify the two specimens X and Y.
ii. State the reason for the behaviour of the field lines in X and Y.

Define mutual inductance between a pair of coils. Derive an expression for the mutual inductance of two long coaxial solenoids of the same length wound one over the other.

The figure below shows planer loops of different shapes moving out of or into a region of the magnetic field which is directed normal to the plane of the loops away from the reader. Determine the direction of induced current in each loop using Lenz's law. Check if you would obtain the same answers by considering the magnetic force on the charge inside the moving loops.

Microwave oven: The spectrum of electromagnetic radiation contains a part known as microwaves. These waves have frequency and energy smaller than visible light and wavelength larger than it. What is the principle of a microwave oven and how does it work? Our objective is to cook food or warm it up. All food items such as fruit, vegetables, meat, cereals, etc., contain water as a constituent. Now, what does it mean when we say that a certain object has become warmer? When the temperature of a body rises, the energy of the random motion of atoms and molecules increases and the molecules travel or vibrate or rotate with higher energies. The frequency of rotation of water molecules is about 2.45 gigahertz (GHz). If water receives microwaves of this frequency, its molecules absorb this radiation, which is equivalent to heating up water. These molecules share this energy with neighbouring food molecules, heating up the food. One should use porcelain vessels and non-metal containers in a microwave oven because of the danger of getting a shock from accumulated electric charges. Metals may also melt from heating. The porcelain container remains unaffected and cool, because its large molecules vibrate and rotate with much smaller frequencies, and thus cannot absorb microwaves. Hence, they do not get eaten up. Thus, the basic principle of a microwave oven is to generate microwave radiation of appropriate frequency in the working space of the oven where we keep food. This way energy is not wasted in heating up the vessel. In the conventional heating method, the vessel on the burner gets heated first and then the food inside gets heated because of transfer of energy from the vessel. In the microwave oven, on the other hand, energy is directly delivered to water molecules which is shared by the entire food.

(i) As compared to visible light microwave has frequency and energy
(a) Frequency is less but energy is more
(b) less than visible light
(c) more than visible light
(d) equal to visible light

(ii) When the temperature of a body rises
(a) the energy of the random motion of atoms and molecules decreases.
(b) the energy of the random motion of atoms and molecules remains same.
(c) the energy of the random motion of atoms and molecules increases
(d) the random motion of atoms and molecules becomes streamlined.

(iii) he frequency of rotation of water molecules is about
(a) 2.45 THz
(b) 2.45 kHz
(c) 2.45 MHz
(d) 2.45 GHz

OR

In the microwave oven
(a) Energy is directly delivered to the food grains.
(b) The vessel gets heated first and then the water molecules collect heat from the body of the vessel
(c) Energy is directly delivered to water molecules which is shared by the entire food
(d) The vessel gets heated first, and then the food grains inside

(iv) Why should one use porcelain vessels and non-metal containers in a microwave oven?
(a) Because it will prevent the food items to become hot
(b) Because it will get too much hot
(c) Because of the danger of getting a shock from accumulated electric charges
(d) Because it may crack due to high frequency

Derive an expression for the electric potential at a point due to an electric dipole. Mention the contrasting features of electric potential of a dipole at a point as compared to that due to a single charge.

A parallel plate capacitor is charged by a battery. After some time the battery is disconnected and a dielectric slab with its thickness equal to the plate separation is inserted between the plates. What change, in any will take place in
i. charge on the plates
ii. electric field intensity between the plates
iii. the capacitance of the capacitor,
iv. a potential difference between the plates and
v. the energy stored in the capacitor? Justify your answer in each case. OR