Tag: physics

Questions Related to physics

State whether true or False 
10 mN is equal to $10^{-3}$ dynes.

physics force and types of force introduction to force what is force? concept of force and its unit

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

Newton (N) is a SI unit of Force while dyne is a CGS unit of force.   


Relation between them is given as 


$1 dyne=1*10^{-3}*1*10^{-2}N$
$1 dyne =10^{-5}N$
$1 N = 10^5 dyne$
$10 \ mN = 10 \times 10^{-3} N= 10^{-2} N = 10^{-2} \times 10^{5} dyne$
$10 \ mN=10^{3}dyne$

Which of the following laws represents the qualitative measure of force?

physics force and types of force introduction to force what is force? concept of force and its unit

  1. Newton's first law of motion

  2. Fleming's right hand rule

  3. Fleming's left hand rule

  4. Zeroth law of thermodynamics

Show answer
Correct Option: A
Explanation:

Newton's first law of motion represents the qualitative measure of force.It states that:

An object remains in the state of rest or of uniform motion in a straight line unless compelled to change that state by an applied unbalanced force.
All objects resist change in their state of motion. The tendency of undisturbed objects to stay at rest or to keep moving with the same velocity is called inertia. This is why, the first law of motion is also known as the law of inertia.

The state of rest or state of motion of a body can be changed by using

physics force and types of force introduction to force what is force? concept of force and its unit

  1. Pressure

  2. Force

  3. Heat

  4. None of these

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Correct Option: B
Explanation:

First law of motion:

A body in rest or a body in motion will continue to do that unless and until an external force is applied on it.
Force will accelerate or decelerate a body.
 

A solenoid coil is wound on a frame of rectangular cross section. If all the linear dimension of the frame are increased by a factor of two and the number of turns per unit length of the coil remains the same, the self-inductance increases by a factor of

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. $4$

  2. $8$

  3. $12$

  4. $16$

Show answer
Correct Option: B
Explanation:

Self inductance, $L = \dfrac{\mu 0 N^2 A}{l}$ _(1)


where N = total number of turns


$n = \dfrac{N}{l}$, where n = number of turns per unit length

$N = nl$ put it in (1)

$L = \dfrac{\mu _0 (n l )^2 A}{l} = \mu _0 n^2 l A$

In the given question n is same
Area will increase by $4$ times
length will increase by $2$ times

$L' = \mu _0 n^2 (2l) (4A) = 8 \mu _0 n^2 lA$

$L' = 8L$ inductance will increased by $8$ times.

The physical quantity which is measured in the unit of Wb $A^{-1}$ is

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. self inductance

  2. mutual inductance

  3. magnetic flux

  4. both (a) and (b)

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Correct Option: D
Explanation:

both (a) and (b) 

self inductance and mutual inductance has same unit both measure magnetic flux per unit area.

The unit of inductance is equivalent to

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. $\dfrac {volt\times ampere}{second}$

  2. $\dfrac { ampere}{volt\times second}$

  3. $\dfrac {volt}{Ampere\times second}$

  4. $\dfrac {volt\times second}{ampere}$

Show answer
Correct Option: D
Explanation:

$As \, \varepsilon \, = \,  L \, \dfrac{dI}{dt},$
$L \, = \, \varepsilon \dfrac{dt}{dI} \Rightarrow \, L \, = \, \dfrac{volt \times second}{ampere}$

What is the SI unit of self-inductance ?

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. Henry

  2. Tesla

  3. Weber

  4. Gauss

Show answer
Correct Option: A
Explanation:

 Henry (symbol H) is the SI derived unit of self-inductance. 

Two concentric co-planar circular loops of radii $r _1$ and $r _2$ carry currents of respectively $i _1$ and $i _2$ in opposite directions (one clockwise and the other anticlockwise.) The magnetic induction at the centre of loops is half that due to $i _1$ alone at the centre. If $r _2 = 2r _1$. the value of $i _2 / i _1$ is 

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. $2$

  2. $\dfrac{1}{2}$

  3. $\dfrac{1}{4}$

  4. $1$

Show answer
Correct Option: D
Explanation:

$\begin{array}{l} B=\frac { { { \mu _{ o } }{ i _{ 1 } } } }{ { 2{ r _{ 1 } } } } -\frac { { { \mu _{ o } }{ i _{ 2 } } } }{ { 2\left( { 2{ r _{ 1 } } } \right)  } }  \ =\frac { { { \mu _{ o } }{ i _{ 1 } } } }{ { 2{ r _{ 1 } } } } -\frac { { { \mu _{ o } }{ i _{ 2 } } } }{ { 4{ r _{ 2 } } } }  \ { B^{ ' } }=\frac { { { \mu _{ o } }{ i _{ 1 } } } }{ { 2{ r _{ 1 } } } }  \ \Rightarrow B=\frac { { { B^{ ' } } } }{ 2 }  \ \Rightarrow \frac { { { \mu _{ o } }{ i _{ 1 } } } }{ { 2{ r _{ 1 } } } } -\frac { { { \mu _{ o } }{ i _{ 2 } } } }{ { 4{ r _{ 1 } } } } =\frac { { { \mu _{ o } }{ i _{ 1 } } } }{ { 4{ r _{ 1 } } } }  \ \Rightarrow \frac { { { \mu _{ o } }{ i _{ 1 } } } }{ { 4{ r _{ 1 } } } } =\frac { { { \mu _{ o } }{ i _{ 2 } } } }{ { 4{ r _{ 1 } } } }  \ \Rightarrow \frac { { { i _{ 1 } } } }{ { { i _{ 2 } } } } =1 \ Hence, \ option\, \, D\, \, is\, \, correct\, \, answer. \end{array}$

When the number of turns in a solenoid is doubled without any change in the length of the solenoid, its self-inductance becomes :

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. Half

  2. Double

  3. Four times

  4. Eight times

Show answer
Correct Option: C
Explanation:

Self-inductance,
$\begin{array}{l}L \propto {N^2}\\therefore \dfrac{{{L _1}}}{{{L _2}}} = {\left( {\dfrac{{{N _1}}}{{{N _2}}}} \right)^2} = {(2)^2} = 4...........{ since,{N _2} = 2{N _1}} \\left[ {{L _2} = 4{L _1}} \right]\end{array}$

Which of the following does not have the same dimensions as the Henry?

introduction to induction electromagnetic induction electromagnetic induction and alternating currents physics

  1. $\dfrac{\text {joule}}{(\text{ampere})^2}$

  2. $\dfrac{\text {tesla} - m^2}{(\text{ampere})^2}$

  3. $\text{ohm-second}$

  4. $\dfrac{1}{\text{Farad-second}}$

Show answer
Correct Option: D
Explanation:

Option $D$ is does not have the same dimensions as the Henry.

So, Option $D$ is correct.