Tag: physics

Questions Related to physics

The radius of the earth is given $6.4\times 10^6 m$. What is the order of magnitude of the size of the earth? 

physics units and measurement: error analysis rounding off digits rounding of digits standard form

  1. $10^6 m$

  2. $6 \times 10^6 m$

  3. $10^7 m$

  4. $5 \times 10^6 m$

Show answer
Correct Option: C
Explanation:

When a number rounded to the nearest power of 10, it is called order of magnitude. Here a number which is less than 5 is taken as 1 and a number greater than 5 is taken as 10. 
As $6.4>10, $ so it would be takes as 10. 
The order of magnitude of earth's size $=10\times 10^6=10^7 m$  

What is the order of magnitude of the distance of a quasar from us if light takes 2.9 billion years to reach us ?  

physics units and measurement: error analysis rounding off digits rounding of digits standard form

  1. $2.7\times 10^{25} m$

  2. $ 10^{25} m$

  3. $10^24 m$

  4. $3\times 10^{25} m$

Show answer
Correct Option: B
Explanation:

Here, time taken $t=2.9$ billion years $=2.9\times 10^9$ years $ =2.9\times 10^9\times (365\times 24\times 3600) s=9.14\times 10^{16} s$
Distance $=$ velocity $\times $ time
or $d=(3\times 10^8)\times (9.14\times 10^{16})=2.74\times 10^{25} m$
As $2.74 <5$ so it will be taken as 1. 
Thus, the order of magnitude of distance $d=1\times 10^{25} m=10^{25} m$

Match the following:

Column - I Column - II
A Deca p $10^3$
B Hecto q $10^6$
C Kilo r $10^1$
D Mega s $10^2$
E Giga t $10^8$
u $10^9$


physics units and measurement: error analysis rounding off digits rounding of digits standard form

  1. A-r, B-s, C-p, D-q, E-u

  2. A-s, B-r, C-p, D-q, E-u

  3. A-r, B-s, C-u, D-q, E-p

  4. A-q, B-s, C-p, D-r, E-u

Show answer
Correct Option: A
Explanation:

Here column-I represents the some prefixes and column-II represents the power of ten corresponding prefixes. 

Deca $=10^1$, hecto =$10^2$, kilo =$10^3$, mega $=10^6$, giga $=10^9$ 
Thus, A-r, B-s, C-p, D-q, E-u

$ 5\times 10^7 \mu s$ is equivalent to ____

physics units and measurement: error analysis rounding off digits rounding of digits standard form

  1. 0.5 s

  2. 5 s

  3. 50 s

  4. 500 s

Show answer
Correct Option: C
Explanation:

We know that  $1\mu s = 10^{-6} \ s$
Thus,  $5\times 10^{7}\mu s = 5\times 10^{7}\mu s\times \dfrac{10^{-6} \ s}{\mu s} = 50 \ s$

The order of magnitude of $379$ is

physics units and measurement: error analysis rounding off digits rounding of digits standard form

  1. $1$

  2. $2$

  3. $3$

  4. $4$

Show answer
Correct Option: B
Explanation:

Order of magnitude of $379$ is $\dfrac { 379 }{ { 10 }^{ 2 } } =3.79<{ 5 }^{ -1 }$    i.e, $379\approx { 10 }^{ 2 }$

order of magnitude $=2$.

With due regard to significant figures, add the following:
a. 953 and 0.324
b. 953 and 0.625
c. 953.0 and 0.324
d. 953.0 and 0.374

physics units and measurement: error analysis rounding off digits rounding of digits standard form

  1. a. $953$; b. $954$ c. $953.3$ d. $953.4$

  2. a. $953$; b. $955$ c. $953.3$ d. $953.4$

  3. a. $952$; b. $954$ c. $953.3$ d. $953.4$

  4. a. $953$; b. $954$ c. $953.3$ d. $952.4$

Show answer
Correct Option: A
Explanation:
a.  $953+0.324=953.324\approx \boxed { 953 } $
b.  $953+0.625=953.625\approx \boxed { 954 } $
c.  $953.0+0.324=953.324\approx \boxed { 953.3 } $
d.  $953.0+0.374=953.374\approx \boxed { 953.4 } $

The coefficient of mutual inductance between two coils depends on

mutual inductance electromagnetic induction electromagnetic induction and alternating currents physics

  1. medium between the coils

  2. separation between the two coils

  3. orientation of the two coils

  4. all of the above

Show answer
Correct Option: D
Explanation:

The flux linked with two coils will depend upon the angle between the two coils. If their planes are parallel, then magnetic flux from one would completely  pass through the other. If the planes are perpendicular, no flux due to any of the coils would flow through the other.

The size of the two coils may be different which will affect the number of lines crossing the coil. The medium, if magnetic, will concentrate the field lines. Thus, all parameters would affect the inductance between them.

Two coils of self inductances 2 mH and 8 mH are placed so close together that the effective flux in one coil is completely linked with the other. The mutual inductance between these coils is:

mutual inductance electromagnetic induction electromagnetic induction and alternating currents physics

  1. 10 mH

  2. 6 mH

  3. 4 mH

  4. 16 mH

Show answer
Correct Option: C
Explanation:

Given,

$L _1=2mH$
$L _2=8mH$
The mutual inductance between coil is 
$M=\sqrt{L _1L _2}$
$M=\sqrt{2\times 8}=\sqrt{16}mH$
$M=4mH$
The correct option is C.

A circular copper disc 10 cm in diameter rotates at 1800 revolution per minute about an axis through its centre and at right angles to disc. A uniform field of induction B of 1 Wb $m^2$ is perpendicular to disc. What potential difference is developed between the axis of the disc and the rim ?

mutual inductance electromagnetic induction electromagnetic induction and alternating currents physics

  1. 0.023 V

  2. 0.23 V

  3. 23 V

  4. 230 V

Show answer
Correct Option: B
Explanation:

Here, 

$l = r = 5\, cm = 5 \times 10^{-2} m,$
B = 1 Wb $m^{-2}$

$ \omega = 2 \pi \left( \dfrac{1800}{60} \right) \, rad \, s^{-1} = 60 \pi \, rad \, s^{-1},$

$\epsilon \, = \, \dfrac{1}{2} Bl^2 \omega \, =\, \dfrac{1}{2} \times 1 \times (5 \times 10^{-2})^2 \times 60 \pi = 0.23 V$

Mutual inductance of two coils can be increased by 

mutual inductance electromagnetic induction electromagnetic induction and alternating currents physics

  1. decreasing the number of turns in the coils

  2. increasing the number of turns in the coils

  3. winding the coils on wooden cores

  4. none of these.

Show answer
Correct Option: B
Explanation:

As M  = $\dfrac{\mu _0N _1N _2A}{l} $ 
i.e M can be increased by increasing the numbers of turns in the coils.