Subjective Question Archive

Hi all,
I have given the link of most of the subjective questions in this blog under the tab "Subjective Question Archive" please visit the page and i hope you will definitely learn something or the other about solving questions in various topics in physics while going through these questions. Most of the questions given came along with their answers and solutions .
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With best wishes for your exams
Physics Expert

Advantages an disadvantages of A.C. over D.C.

ADVANTAGES

1. The generation of A.C. is cheaper than that of D.C.
2. A.C. machines are simple , robust and do mot require much attention for their repairs and maintainance during their use.
3. Wide range of voltages are obtained by the use of transformer.
4. The magnitude of current can be reduced by using an inductance or a conductor without any appreciable loss of energy
5. A.C. can easily be converted into D.C. with the help of rectifiers.
6. When A.C. is supplied at higher voltages in long distance transmission , the line losses are small compared to a D.C. transmission

DISADVANTAGES

1. Peak value of A.C. is high and it is dangerous to use so better insulation is required.
2. It attracts person who touches it unlike D.C. which gives a repelling shock.
3. An A.C. is transmitted from surface of the conductor and hence need several strands of thin wires insulated from each other.

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PMT Focus : Assertion reason type questions

The following questions consists of two statements , Assertion and Reason. While answering these questions choose any of the following four responses
A. If both assertion and reason are true and the reason is correct explanation of assertion.
B. If both assertion and reason are true but reason is not a correct explanation of assertion.
C. If assertion is true and reason is false.
D. If both assertion and reason are false.

1. Assertion : In series LCR circuit , resonance occurs only at one frequency.
    Reason :  At this frequency inductive reactance is equal to capacitive reactance.
(a) A
(b) B
(c) C
(d) D

2. Assertion: Insulators do not allow the flow of current through themselves.
    Reason: They have no free charge carriers.

(a) A

(b) B

(c) C

(d) D

3. Assertion : When temperature of cold junction of a thermocouple is lowered , the value of neutral temperature of this thermocouple is raised
 Reason : When the difference of temperature of two junction is raised , more thermo e.m.f. is produced.

(a) A

(b) B

(c) C

(d) D

4. Assertion : If two parallel wires , hanging freely are connected to a battery in series , they come closer to each other.
Reason : Force of attraction acts between two wires crying charge 

(a) A

(b) B

(c) C

(d) D

5. Assertion : If an electron and proton enter an electric field with equal energy , then path of electron is more curved then that of electron.
 Reason : electrons has a tendency to form curve.

(a) A

(b) B

(c) C

(d) D

Answer:

1. a

2. a

3. d  here both assertion and reason are not true

4. d when two long parallel wires are connected to battery in series they carry current in opposite direction and hence repel each other.

5. d

Surface tension fact file

1. Those factors which increases cohessive forces between liquid molecules increases surface tension and those decreases cohesive forces decreases surface tension.
2. If impurity is completely soluble , then on mixing it in the liquid , its surface tension increases.
3. With the increase in temperature surface tension decreases.
4. Surface tension depands on the medium present on other side of the liquid surface.
5. The surface tension decreases due to electrification.
6. On mixing partial soluble impurities in a liquid , its surface tension decreases like mixing of detergent in water decreases surface tension of water.

Challenging mechanics problem : Kinematics

Question :
A body of mass m rests on horizontal table which has coefficient of static friction μ . It is desired to move the body by applying minimum possible force F. Find the magnitude and direction of the force F to which it has to be applied.
Solution :
For solution visit this link

Problem on Bohr atom model

Question:
A particle of charge equal to that of electron and mass 208 times the mass of electron (-meson)moves in a circular orbit around a nucleus of charge +3e (assume mass of nucleus to be infinite). Assuming that the Bohr atom model is applicable to this system
(a) derive an expression for the radius of the nth Bohr orbit
(b) find the value of n for which the radius of the orbit is approximately the same as that of the first Bohr orbit for the hydrogen atom
(c) find the wavelength of the radiation emitted when  -meson jumps from the third orbit to the first orbit (Rydberg constant = 1.097 x 107 m-1)  

Solution:

For solution click this link