Tag: physics

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Questions Related to physics

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

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? 

  1. $10^6 m$

  2. $6 \times 10^6 m$

  3. $10^7 m$

  4. $5 \times 10^6 m$
Reveal answer Fill a bubble to check yourself
C Correct answer
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 $=10\times 10^6=10^7 m$  

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

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

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

  2. $ 10^{25} m$

  3. $10^24 m$

  4. $3\times 10^{25} m$
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $d=1\times 10^{25} m=10^{25} m$

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

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 $10^9$


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

  2. <span>A-s, B-r, C-p, D-q, E-u</span>

  3. <span>A-r, B-s, C-u, D-q, E-p</span>

  4. <span>A-q, B-s, C-p, D-r, E-u</span>
Reveal answer Fill a bubble to check yourself
A Correct answer
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

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

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

  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. $952.4$
Reveal answer Fill a bubble to check yourself
A Correct answer
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 } $
Multiple choice mutual inductance electromagnetic induction electromagnetic induction and alternating currents physics

The coefficient of mutual inductance between two coils depends on

  1. medium between the coils

  2. separation between the two coils

  3. orientation of the two coils

  4. all of the above
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

Multiple choice mutual inductance electromagnetic induction electromagnetic induction and alternating currents physics

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:

  1. 10 mH

  2. 6 mH

  3. 4 mH

  4. 16 mH
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

Multiple choice mutual inductance electromagnetic induction electromagnetic induction and alternating currents physics

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 ?

  1. 0.023 V

  2. 0.23 V

  3. 23 V

  4. 230 V
Reveal answer Fill a bubble to check yourself
B Correct answer
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},$

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