CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Value Based Questions 5 Mark Questions 2021
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CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Value Based Questions 5 Mark Questions 2021
12th Standard CBSE
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Reg.No. :
Physics
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A rectangular coil of n turns each of area A, carrying current I, when suspended in a uniform magnetic field B, experiences a torque
\(\tau =nI \ BA \ sin\theta \)
Where is \(\theta \) the angle which a normal drawn on the plane of coil makes with the direction of magnetic field. This torque tends to rotate the coil and bring it in an equilibrium position. In the stable equilibrium state, the resultant force on the coil is zero. The torque on the coil is also zero and the coil has minimum potential energy.
Read the above passage and answer the following questions:
(i) In which position, a current carrying coil suspended in uniform magnetic field experiences
(a) minimum torque and
(b) maximum torque?
(ii) a circular coil of 200 turns, radius 5 cm carries a current of 2.0 A. It is suspended vertically in a uniform horizontal magnetic field of 0.20 T, with the plane of the coil making an angle with \(60°\) the field lines. Calculate the magnitude of the torque that must be applied on it to prevent it from turning.
(iii) what is the basic value displayed by the above study?(a) -
Shikhaj was working on a project for science exhibition. He considered a capacitance of 2\(\mu F\) having a capacity of operating under 1kV potential. When he reached to shop, he found that the shopkeeper is having a capacitors of 1 \(\mu F\) of 400 V rating. Shikhaj calculated minimum number of capacitances of 1 \(\mu F\) each, so he could arrange to form a capacitor of 2 \(\mu F\) .
Answer the following questions based on the above information:
(i) What are the calculations done by Shikhaj?
(ii) What do you think of Shikhaj?(a) -
In Pradeep's classroom, the fan was running very slowly. Due to which, his teacher was sweating and was restless and tired.All his classmates wanted to rectify this. They called an electrician who came and changed the capacitor only, after which the fan started running fast.
Answer the following questions based on the above information:
(i) What energy is stored in the capacitor and where?
(ii) A thin metal sheet is placed in the middle of a parallel plate capacitor. What will be the effect on the capacitance?
(iii) What values did the classmates have?(a) -
Geeta has dry hair. A comb ran through her dry hair attracts small bits of paper. She observes that Neeta with oily hair combs her hair, the comb could not attract small bits of paper. She consults her teacher for this and gets the answer. she then goes to the junior classes and shows this phenomenon as a Physics experiment to them.
Read the above passage and answer the following questions.
What according to you are the values displayed by Geeta?
Explain the phenomenon involved.(a) -
As it is known that all matter is made up of atoms/ molecules. Every atom consists of a central core, called the atomic nucleus, around which negatively charged electrons revolve in circular orbits. Every atom is electrically neutral containing as many electrons as the number of protons in the nucleus. All the materials are electrically neutral, they contain charges, but their charges are exactly balanced.
Read the above passage and answer the following questions.
Everybody whether a conductor or an insulator is electrically neutral. Is it true?
Charging lies in charge imbalance, i.e. excess charge or deficit charge, comment.
How do you visualise this principle being applied in our daily life?(a)
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CBSE 12th Standard Physics Subject Electrostatic Potential And Capacitance Value Based Questions 5 Mark Questions 2021 Answer Keys
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As \(\tau =nIBA \ sin \ \theta ,\ therefore,\ (i) \ \tau =0, \ when \ sin\theta =0 \ or \ \theta =0°, \ i.e.\)when the plane of coil is perpendicular to the direction of magnetic field. (ii) \(\tau =\) maximum, when \(sin \ \theta \)=maximum=1 or \(\theta =90°\)
\({ \tau }_{ max }=nIBA\times 1=nIBA\)
It will be so when the plane of coil is parallel to the direction of magnetic field.
(ii) Here, n = 200; r = 0.05m; I = 2.0 A; B = 0.20 T; \(\theta =90°-60°\)=\(30°\)
\( \tau =nIBA \ sin \ \theta ,\ therefore,\ (i) \ \tau =0, \ when \ sin\theta =0 \ or \ \theta =30°-60°, \ i.e.,\)
\( \\ { \tau }_{ max }=nIBA\times 1=nIBA\)
\( \tau =nIBA \ sin \ \theta =nIB({ \pi r }^{ 2 })sin\theta =200\times 2.0\times 0.20\left[ (22/7)\times { \left( 0.05 \right) }^{ 2 } \right] \times sin30°\)
\(=0.314\quad N-m=0.31\ Nm\)
(iii) From the above study, we find that when potential energy of the coil is minimum, both force and torque acting on the coil are zero. The same is true in real life. a person who is humble and boasts of nothing, would be a happy person, with no pulls and pressure of life. -
(i) Total potential difference across each row = 1000 V
Potential difference across each capacitor = 400 V
Number of capacitors in series,
\(n=\frac { 1000 }{ 400 } =2.5\ \approx \ 3\)
Capacitance of capacitors in series, Cs = \(\frac { 1 }{ 3 } \mu F\)
Let m be rows of capacitors, for an equivalent capacitance of \(2\mu F\), we have
\(m\times \frac { 1 }{ 3 } =2\Rightarrow m=6\)
Hence, total number of capacitance required
= m x n = 6 x 3 = 18
Total 6 rows of capacitor in parallel with three capacitors in each row.
(ii) We think that Shikhaj knows the value of money and have the ability to calculate scientifically in daily life. -
(i) Electrical energy is stored in the capacitor.It is stored in the dielectric.
(ii) No effect. When the metal sheet is placed in the middle the new arrangement is equivalent to a old combination of two capacitors each of plate separation \(\frac{d}{2}\) and hence capacitance 2C.
\({ C }_{ S }=\frac { 2C\times 2C }{ 2C+2C } =C\)
(iii) Team work, concern, respect to teacher and responsibility. -
The values displayed by Geeta are curiosity, leadership and compassion.
Frictional electricity Frictional electricity is the electricity produced by rubbing two suitable bodies and transfer of electrons from one body to other.
Further, if the hair are oily or wet, then the friction between the hair and comb reduces and the comb will not attract small bits of paper. -
Yes, it is true. Every conductor/insulator is electrically neutral, as it contains equal amounts of positive charge and negative charge.
This statement is true. Charging lies in charge imbalance. When a body loses some electrons, it becomes positively charged because it has excess of protons over electrons. The reverse is also true.
Nature/God has created the universe. In original, all bodies are neutral with no forces of attraction/repulsion. When interests of any two persons clash (i.e. two bodies are rubbed against each other), they become charged. From the charging, the forces of attraction/repulsion arises, i.e. pulls and pressures of life.
Nature/God wants us to live in peace without stress and tensions in life. We get charged over petty things in life and invite all sorts of pulls, pressures and tensions.
