CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Value Based Questions 5 Mark Questions With Solution 2021
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CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Value Based Questions 5 Mark Questions With Solution 2021
12th Standard CBSE
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Reg.No. :
Physics
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When an electric dipole of moment \(\left| P \right| \) = q \(\times\) 2a is held at an angle \(\theta\), with the direction of uniform external electric field E, a torque \(\tau \) = pE sin\(\theta\) acts on the dipole. This torque tries to align the electric dipole in the direction of the field. When p is along E, \(\theta=0^{o}\), \(\tau \) = pE sin\(0^{o}\) = zero.
Read the above passage and answer the following questions.
(i) What is the direction of torque acting on an electric dipole held at a angle with uniform external field?
(ii) An electric dipole of length 10 cm having charge \(\pm 6\times { 10 }^{ -3 }\), C placed at \(30^{o}\) with respect to a uniform electric field experiences a torque of magnitude \(6\sqrt { 3 } \) N-m. Calculate magnitude of electric field.
(iii) What is the physical significance of this concept in our day-today life?(a) -
Two persons are standing under a tree and another person near them is inside a car. They were arguing about going out for a movie or to the beach, when a lightning struck the tree with some force. The person inside the car notices his friends satnding under the tree are affected by lightning, he comes out and takes them to the nearby hospital.
Why the person in the car was not affected by lighting?
What quality do you find the person inside the car?
Explain the process that takes place during lighting.
If the total charge enclosed by a surface is zero, then what will be the electric flux over the surface?(a) -
The surface integral of electrostatic field E produced by any source over any closed surface S enclosing a volume V in vacuum, i.e. total electric flux over the closed surface S in vacuum is \(1/{\epsilon}_{0}\) times the total charge Q contained inside S, i.e.
\({\phi}_{E}=\oint E.dS={{Q}\over{{\epsilon}_{0}}}\)
The charges inside S may be point charges or even continuous charge distributions. There is no contribution to "total electric flux from the charges outside S. Further, the location of Q inside S does not affect the value of surface integral.
Read the above passage and answer the following questions
What are the SI units and dimensions of electric flux?
A closed surface in vacuum encloses charges -q, + 3q and +5q. Another charge + 4q lies outside the surface. What is total electric flux over the surface?
A point charge a lies inside a spherical surface of radius r. How will the electric flux be affected, if, radius of the sphere is doubled?
What values of life do you learn from this theorem?(a) -
An old woman who had suffered from a heat stroke was taken to the hospital by her grandson who is in class XII. The grandson has studied in Physics that, how to save person who is suffering from a heat stroke, regular beating of the heat is to be restored by delivering a jolt to the heart using a defibrillator, whose capacity is 70 μF and charged to a 'potential of 5000 V and energy stored is 875 J, 200 J of energy is passed through a person's body in a pulse lasting 2 ms. The old woman gets paniced and refuses to be treated by defibrillator. Her grandson then explained to her the process that would be adopted by medical staff and how the result of that would bring her back to normalcy. The woman was then treated and was back to normal. Answer the following questions based on the above information.
(i) What according to you are the values displayed by the grandson?
(ii) What will be the net charge of the capacitor in defibrillator?(a) -
A man travelling in a car during heavy rain and thunderstorm, sees a boy standing under a tree. He immediately stops his car and asks the boy to get inside the car and saves him from a possible natural calamity. Answer the following questions based on the above information.
(i) What danger did the boy had while standing under the tree during the thunderstorm?
(ii) How is it safer inside the car during such weather?
(iii) What according to you are the values displayed by the man to help the boy?
(iv) Give another example from everyday life situations which represent display of similar values.(a)
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CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Value Based Questions 5 Mark Questions With Solution 2021 Answer Keys
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(i) \(\tau \) = pE sin\(\theta\) can be rewritten in vector form as \(\tau \) = p \(\times\) E
Therefore, the direction of torque \(\tau \) is perpendicular to both p and E. It is determined by right handed screw rule.
(ii) Here, 2a = 10 cm = 10-1 m,
q = \(6\times { 10 }^{ -3 }\) C, \(\theta=30^{o}\)
\(\tau \) = \(6\sqrt { 3 } \) N-m,E = ?
From \(\tau \) = pE sin\(\theta\) = q(2a)E sin\(\theta\)
\(6\sqrt { 3 } \) = \(6\times { 10 }^{ -3 }\left( { 10 }^{ -1 } \right) \) Esin\(30^{o}\)
\(6\sqrt { 3 } \) = \(6\times { 10 }^{ -4 }\times E \times\frac { 1 }{ 2 }\Rightarrow6\sqrt { 3 }=3\times{ 10 }^{ -4 }E\)\(\Rightarrow\) E = \(\frac { 6\sqrt { 3 } }{ 3\times { 10 }^{ -4 } } =2\sqrt { 3 } \times { 10 }^{ 4 }\) NC-1
(iii) From the given paragraph, we find that electric dipole held in an external electric field will be in stable equilibrium only when it is aligned along the external electric field. The same is true in day-today life.
At your work place, your boss always tries to align you along his/her paln. Your job/position is secured/stable after you are perfectly aligned and your personal whims are at the lowest ebb. -
Due to electrostatic shielding, the person in the car was not affected (electric field inside the metallic body is zero).
Helping others, taking a quick decision as to wha is to be done, in case, he is unaware or unable to do on his own.
Lighting is a massive electostatic discharge between electrically charged regions within the clouds or between a cloud and the earth's surface.
As \(\phi=\frac { q }{ { \varepsilon }_{ 0 } }\), therefore, electric flux over the surface will be zero because net charge enclosed by a surface is zero. -
SI units of electric flux is N-m2C-1.
Dimensional formula of electric flux is [ M1L1T-3A-1].
\(\phi={{\sum {q}_{inside}}\over{{\epsilon}_{0}}}={{-q+3q+5q}\over{{\epsilon}_{0}}}={{7q}\over{{\epsilon}_{0}}}\)
As \(\phi={{q}\over{{\epsilon}_{0}}},\) electric flux is not affected by area/shape of the surface. So, the electric flux remains unaffected.
This theorem emphasis that total normal flux from the surface depends only on algebraic sum of charges enclosed by the surface, irrespective of their location. The charges outside the surface do not affect the electric flux. In day-to-day life, the theorem implies that the knowledge you can import depends only on what you have stored within you. You
cannot emanate what you have not absorbed or what lies outside your reach?
In the examination, you can write what you have learnt by heart? Extraneous help from outside by unfair means will never serve your purpose. -
(i) Presence of mind, knowledge of subject, concern for his grandmother, empathy helping and caring.
(ii) The net charge of the capacitor in defibrillator is given by
Q = CV [where, C = capacitance V = voltage]
⇒ Q = 70\(\times\)10-6\(\times\)5000 = 35\(\times\)10-2C -
(i) Trees often being much taller than surrounding structures will attract lightning and the tree can get, on fire. The boy might get electrocuted. Also, if the lightning strikes the tree, then the tree might fall on the boy.
(ii) During thunderstorms, it is safer to sit inside a car because car has a metallic body that does not allow the lightning to hit the person sitting inside the car. We know that charges always reside on the surface of metal. Inside the conductor, charge is zero. If lightning strikes the car during a thunderstorm, the charges will be distributed on the surface of the metal body of car. No charges will exist inside the car. Hence, the person sitting inside the car is considered safe are the values displayed.
(iii) Helpfulness, Compassion, General awareness, service to others are the values displayed.
(iv) Advising a person who is doing repair work on air condition system without switching OFF the mains.
Stopping a person entering nuclear medicine ward in a hospital without proper protection or precautions.
