# CBSE (Science) Class 12 - CBSE Important Questions for Physics

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Write two important advantages of reflecting telescope over a refracting telescope.

Appears in 12 question papers
Chapter: [0.09] Ray Optics and Optical Instruments
Concept: Optical Instruments > Telescope

State the two Kirchhoff’s rules used in electric networks. How are there rules justified?

Appears in 10 question papers
Chapter: [0.03] Current Electricity
Concept: Kirchhoff’s Rules

In a single slit diffraction experiment, the width of the slit is made double the original width. How does this affect the size and intensity of the central diffraction band?

Appears in 10 question papers
Chapter: [0.1] Wave Optics
Concept: Diffraction of Light > The Single Slit

Define a wavefront

Appears in 10 question papers
Chapter: [0.1] Wave Optics
Concept: Huygens' Principle

Give the truth table and circuit symbol for NAND gate

Appears in 10 question papers
Chapter: [0.14] Semiconductor Electronics - Materials, Devices and Simple Circuits
Concept: Digital Electronics and Logic Gates

Four point charges Q, q, Q and q are placed at the corners of a square of side 'a' as shown in the figure. Find the

1) resultant electric force on a charge Q, and

2) potential energy of this system.

Appears in 9 question papers
Chapter: [0.01] Electrostatic Potential and Capacitance
Concept: Potential Energy of a System of Charges

Define electric flux.

Appears in 9 question papers
Chapter: [0.02] Electric Charges and Fields
Concept: Electric Flux

If the point charge is now moved to a distance 'd' from the centre of the square and the side of the square is doubled, explain how the electric flux will be affected.

Appears in 9 question papers
Chapter: [0.02] Electric Charges and Fields
Concept: Applications of Gauss’s Law

Use Gauss' law to derive the expression for the electric field (vecE)due to a straight uniformly charged infinite line of charge density λ C/m.

Appears in 9 question papers
Chapter: [0.02] Electric Charges and Fields
Concept: Applications of Gauss’s Law

Draw a graph to show the variation of E with perpendicular distance r from the line of charge.

Appears in 9 question papers
Chapter: [0.02] Electric Charges and Fields
Concept: Applications of Gauss’s Law

Find the work done in bringing a charge q from perpendicular distance r1 to r2 (r2 > r1)

Appears in 9 question papers
Chapter: [0.02] Electric Charges and Fields
Concept: Applications of Gauss’s Law

Two electric bulbs P and Q have their resistances in the ratio of 1 : 2. They are connected in series across a battery. Find the ratio of the power dissipation in these bulbs

Appears in 9 question papers
Chapter: [0.03] Current Electricity
Concept: Combination of Resistors - Series and Parallel

A 10 V cell of negligible internal resistance is connected in parallel across a battery of emf 200 V and internal resistance 38 Ω as shown in the figure. Find the value of current in the circuit. Appears in 9 question papers
Chapter: [0.03] Current Electricity
Concept: Cells, Emf, Internal Resistance

Define the term 'conductivity' of a metallic wire. Write its SI unit.

Appears in 9 question papers
Chapter: [0.03] Current Electricity
Concept: Electrical Resistivity and Conductivity

The susceptibility of a magnetic material is 0·9853. Identify the type of magnetic material. Draw the modification of the field pattern on keeping a piece of this material in a uniform magnetic field.

Appears in 9 question papers
Chapter: [0.04] Magnetism and Matter
Concept: Magnetic Properties of Materials

A proton and an electron travelling along parallel paths enter a region of uniform magnetic field, acting perpendicular to their paths. Which of them will move in a circular path with higher frequency?

Appears in 9 question papers
Chapter: [0.05] Moving Charges and Magnetism
Concept: Motion in Combined Electric and Magnetic Fields > Cyclotron

A bar magnet of magnetic moment 6 J/T is aligned at 60° with a uniform external magnetic field of 0·44 T Calculate

a) the work done in turning the magnet to align its magnetic moment

i) normal to the magnetic field,

ii) opposite to the magnetic field, and

b)  the torque on the magnet in the final orientation in case (ii).

Appears in 9 question papers
Chapter: [0.05] Moving Charges and Magnetism
Concept: Magnetic Diapole

An iron ring of relative permeability µr has windings of insulated copper wire of n turns per meter. When the current in the windings is I, find the expression for the magnetic field in the ring.

Appears in 9 question papers
Chapter: [0.05] Moving Charges and Magnetism
Concept: Solenoid and the Toroid - the Toroid

The teachers of Geeta’s school took the students on a study trip to a power generating station, located nearly 200 km away from the city. The teacher explained that electrical energy is transmitted over such a long distance to their city, in the form of alternating current (ac) raised to a high voltage. At the receiving end in the city, the voltage is reduced to operate the devices. As a result, the power loss is reduced. Geeta listened to the teacher and asked questions about how the ac is converted to a higher or lower voltage.

1) Name the device used to change the alternating voltage to a higher or lower value. State one cause for power dissipation in this device.

2) Explain with an example, how power loss is reduced if the energy is transmitted over long distances as an alternating current rather than a direct current.

3) Write two values each shown by the teachers and Geeta.

Appears in 9 question papers
Chapter: [0.06] Alternating Current
Concept: Transformers

A device X is connected across an ac source of voltage V = V0 sin ωt. The current through X is given as

I = I_0 sin (omega t + pi/2 )

1) Identify the device X and write the expression for its reactance.

2) Draw graphs showing the variation of voltage and current with time over one cycle of ac, for X.

3) How does the reactance of the device X vary with the frequency of the ac? Show this variation graphically.

4) Draw the phasor diagram for the device X.

Appears in 9 question papers
Chapter: [0.06] Alternating Current
Concept: Peak and Rms Value of Alternating Current Or Voltage
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