### HS XII Electrostatics year-wise questions

2019

1. Mention one similarity between Coulomb force and gravitational force acting  between two stationary charges. [Mark-1]
2. Define one coulomb charge. Two point charges at a distance r in air exert a force F on each other. At what distance will these charges experience the same force F in a medium of dielectric constant k ? [Mark-1+1=2]
3. There is an electric dipole on the x-y plane. Its dipole moment is 4 x 10-9Cm . On the same plane there is also a uniform electric field  of magnitude 5 x 104 N/C . If the axis of the dipole makes an angle 300 with the electric field, calculate the magnitude ot the torque acting on the dipole and also mention the direction of torque [Mark-2+1=3]
4. The capacity of a parallel plate capacitor with air is 18 pF.  When a dielectric material is inserted in the space between the plates, its capacity becomes  108 pF. Calculate the permittivity of the material. What is the material ?  [Mark-2+1=3]

2018

1. Which experiment established the fact that electric charge is quantized ? [Mark-1]
2. Give the statement of Coulomb’s law for the force between two point charges. Write this law in vector notation for two point charges of same magnitude and opposite sign separated by a distance r in vacuum. [Mark-1+1=2]          (or)
3. Two point charges 0.01/μC and -0.01/μC are placed 10cm apart in vacuum. Calculate the magnitude of electric field intensity at the middle point of the line joining the charges and mention its direction.           [Mark-1+1=2]
4. Apply Gauss’s law to derive the expression for electric field intensity due to an infinitely long straight uniformly charged wire. What is the direction of the field intensity if it is positively charged ?                     [Mark-2+1=3]       (or)
5. Derive the expression for field intensity due to an electric dipole in vacuum for points on its axis. Compare the variation of field intensity with distance for an electric dipole and a point charge when both are kept in vacuum. [Mark-2+1=3]
6. A 600μF capacitor is charged by a 200V supply. It is then disconnected from the supply and is connected to another uncharged 600μF capacitor. How much electrostatic energy is lost in the process ?    [Mark-3]
7. In the diagram below , a particular of mass  “m” and charge (-q) initially moving along X-axis with velocity “vx” enters the region between two charged plates. The length of the plate system is “L” and uniform electric field between the plates is “E”. What is the vertical deflection of the particle at the far edge of the plate ? [Mark-3]

2017

1.      The product of permeability of free space and permitivity is —
(Choose the right option)
(i) c              (ii) c-1              (iiij c2                (iv )c-2    where c is velocity of light. [Mark-1]
2. In an electric field a unit positive charge is displaced from one point to another point along a straight line of length 2 cm and the work done is 2mJ . If it is displaced along a parabolic path . between the same points of length 5 cm, what will be the work done ?    [Mark-1]
3. Three electric point charges qo  ,  q1 and q2 are at distances r0, r and r2  respectively with respect to same origin. What is the force on charge q0 in the field of charges q1 and q2 ?[Mark-2]
4. The volume charge density within a volume Vis ρ(r). What is the force on a small test charge q0 placed outside the volume having position vector r0 with respect to the same origin considered to specify the position vector of the charge distribution within the volume. [Mark-2]
5. What is the net electric flux through a closed surface surrounding an electric dipole ? Derive the expressions for electric field intensity both inside and outside a uniformly charged spherical cell. What is the total charge enclosed by a closed surface if the electric flux entering and leaving the
surface are 20000 N/Cm2 and 30000 N/Cm2 respectively. Given∈0= 8.85x 10-12 C2N~1 m 2 .   [Mark-1+3+1=5]                             (or)
6. Why is an insulator sometimes called a dielectric ? What is the main difference between free and bound charge ? Generally one of the two plates of a Capacitor System is earthed, why? Derive the expression for the energy stored in a charged capacitor.           [Mark-1+1+1+2=5]

### Marking pattern for AHSEC Physics ,2019

Assam higher secondary education council announced new marking pattern for the subject physics 2019 . Marking pattern will be same for unit 1 ,unit 3 , unit 4, unit 5, unit 6, unit 7 and unit 9 . For unit 2 and unit 8 , 1 mark is increased  and for unit 10 2 mark is  decreased . Full marking scheme is given below

. ncert_xi_11

ncert_xi_08

ncert_xi_10

NCERT 11 U 9

ncert_xii_7

### Important questions for Class XII -Chapter 8 – Electromagnetic waves

Dear students , some important questions are porvided with answers of -Chapter 8 – Electromagnetic waves of class XII

1 mark questions —-

1) Write down ihe expression for velocity of an electromagnetic wave in free space .
2) According to Ampere’s circuital law , what is its limitation ?
3) Which experiment confirmed the existence of electro magnetic waves?
4) Write down the equation of Ampere- Maxwell law.
5) Out of four Maxwell’s equations, which equation establishes non existence of magnetic monopolc?
6) Cite the range of visible spectrum in terms of wave length.
7) Which radiation of electromagnetic spectrum has the shortest wave length?
8) Which part of electromagnetic spectrum carries heat energy?
9) Name the part of electromagnetic spectrum which is suitable for radar system used in aircraft navigation.
10) Name the part of the electromagnetic spectrum of wavelength 10¯² m and mention its one application.
11) The oscillating magnetic field in plane electro magnetic wave is given by
By = 8 x 10-6sin[2x 10 ¹¹t + 300πx ]T Find the wave length of the wave.
12) Reference to problem 11 write down the expression for the oscillating electric field.
13) Identify the electromagnetic radiation as per wavelength
i) 1mm  ii) 10¯¹² m
electromagnetic spectrum having shorter wave length.
16) From the following identify the electromagnetic waves having the (i)Maximum (ii) Minimum frequency
(i) Radio waves (ii) Visible light (iii) Gamma ray  (iv) Microwaves
(v) Ultraviolet rays and (vi) Infrared rays
17) Give one use of ultraviolet radiation.
18) Name two gases which absorb infrared radiation.
19) Name one gas which absorb UV radiation.

2 marks questions —-

1) Sketch a schematic diagram depicting electric and magnetic fields for an electromagnetic wave propagating along the Z-direction. How is velocity related to ε0 and μ0 ?
2) Describe in brief the concept of displacement current.
3) Can we expect a magnetic field in space in absence of conduction current? – Explain in brief.
4) What is radiation pressure ? Why we do not feel radiation pressure when sunlight falls on us ?
5) Write down the four Maxwell’s equations.

3  marks questions —-

1. What are γ-rays? Give two important properties of γ-rays. Depict the range of wave length of γ-rays. 1+1+1=3
2. What are X-rays? Give two important properties and uses of X-rays.
1+1+1=3
3. What are micro waves? Explain the principle of a microwave oven.1+2=3

4. Establish Amperes Maxwell equation 3

5. Write down various uses of radio waves 3

6. Give some uses of ultra violet rays . How human can be protected from it ? 3

### Homework for XI/group A/SHIKSHA/Saturday/29-09-2018

Q1.  A force of 200 N is applied to a block of mass 20 kg on an inclined plane at 53 º with the horizontal .

(i)  What will be the acceleration of the block in downward direction ?

(II) How much force is required to move it in up along the plane ?

(iii) How much force is required to keep the body at rest on the inclined plane ?

Q3. A 20 kg block is initially at rest on a rough horizontal surface. A horizontal   force of 75 N is required to set the block in motion. After it is in motion, ahorizontal force of 60 N is required to keep the block moving  with constant speed. Find the coefficient of static  and kinetic friction .

Q4. A body of 5 kg weight kept on a rough inclined plane of angle 30º starts  sliding with a constant velocity. Then find the coefficient of friction . (assume  g = 10 m/s²)

Q5. Define the following terms

Sliding friction , limiting friction , angle of friction , coefficient of kinetic friction , angle of repose .

### Homework for XII/group B/VIDYARTHI/Friday/28-09-2018

Q1. An AC is given as   i = 10 sin ωt  with .0.02 sec as time period . Draw the AC showing the mean value and RMS value .

Q2. Prove that mean value for the full cycle of an AC is zero .

Q3. The RMS voltage  of the power supply that we use in India is 220 volt . What will be it’s peak value ? Also find the mean value .

Q4. Why AC is dangerous ?

Q5.  An AC   i = 10 sin 314t  is connected to a resistor of resistance 10 Ω   . Find the potential drop across the resistor .

Q6.  An AC   i = 10 sin 314t  is connected to an inductor  of self induction of  10 Henry  . Find the potential drop across the inductor .

Q7.  An AC   i = 10 sin 314t  is connected to a capacitor of 10 μF   . Find the potential drop across the capacitorr .

Q8. Draw the graph showing the variation between

(I) inductive reactance and angular frequency

(ii) capacitive reactance and angular frequency