Tag: physics

Questions Related to physics

A square coil of side 0.5$\mathrm { m }$ has movable side It is placed such that its plane is perpendicularuniform magnetic field of induction 0.2$\mathrm { T }$ . If all sides are allowed to move with a speed of 0.1for 4 sec outwards, average indaced emf is

motional emf physics

  1. Zero

  2. 0.01$\mathrm { V }$

  3. 0.028$\mathrm { V }$

  4. 0.072$\mathrm { V }$

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Correct Option: D

The amplitude of a magnetic field, which is part of a harmonic electromagnetic wave in vacuum, is  $\mathrm { B } _ { 0 } =510\mathrm { nT } .$  What is the amplitude of the electric field of the wave? 

motional emf physics

  1. $140 \mathrm { NC } ^ { - 1 }$

  2. $153 \mathrm { NC } ^ { - 1 }$

  3. $163 \mathrm { NC } ^ { - 1 }$

  4. None of these

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Correct Option: B

A  $1\mathrm { m }$  long conducting rod rotates with an angular frequency of  $400\mathrm { rad } \mathrm { s } ^ { - 1 }$  about an axis normal to the rod passing through its one end. The other end of the rod is in contact with a circular metallic ring. A constant magnetic field of  $0.5\mathrm { T }$  parallel to the axis exists everywhere.Calculate the e.m.f developed between the center and the ring?

motional emf physics

  1. $100 \mathrm { V }$

  2. $101 \mathrm { V }$

  3. $102 \mathrm { V }$

  4. $103 \mathrm { V }$

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Correct Option: A

A charged particle enters in a uniform magnetic field with velocity at an angle of ${ 60 }^{ o }$ with the magnetic field. The pitch of helical path is x, the radius of helix is 

motional emf physics

  1. $\dfrac { x }{ 2\sqrt { 3 } x } $

  2. $\dfrac { 2x }{ \sqrt { 3 } \pi } $

  3. $\dfrac { \sqrt { 3 } x }{ \pi } $

  4. $\dfrac { \sqrt { 3 } x }{ 2\pi } $

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Correct Option: D

When a charged particle is projected perpendicular to a magnetic field then the

motional emf physics

  1. Velocity of the particle remain constant

  2. Momentum of the particle remain constant

  3. Kinetic energy of the particle remain constant

  4. Path of particle is straight line

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Correct Option: C

A $0.1m$ long conductor carrying a current of $50A$ is perpendicular to a magnetic field of $1.21mT$. The mechanical power to move the conductor with a speed of $1m{s}^{-1}$ is

motional emf physics

  1. $0.25mW$

  2. $6.25mW$

  3. $0.625W$

  4. $1W$

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Correct Option: B
Explanation:

Mechanical power required $=$ electrical power expended due to the induced emf 

                                               $= (Blv) \times I \ =( 0.00121 \times 0.1 \times 1 ) \times 50\ =6.25 m W $

A non conducting ring having charge q uniformly distributed over its circumference is placed on a rough horizontal surface. A vertical time varying magnetic field $B=4t^2$ is switched on a time $t=0$. Mass of the ring is m and radius is R. The ring starts rotating after $2$ seconds. The coefficient of friction between the ring and the tablets.

motional emf physics

  1. $\displaystyle\frac{4qmR}{g}$

  2. $\displaystyle\frac{2qmR}{g}$

  3. $\displaystyle\frac{8qR}{mg}$

  4. $\displaystyle\frac{qR}{2mg}$

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Correct Option: C

Which waves are used in sonography?

physics range of hearing sound: production of sound audible, infrasonic and ultrasonic sounds different sounds

  1. Microwaves

  2. Infrared rays

  3. Radio waves

  4. Ultrasonic waves

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Correct Option: D
Explanation:

Ultrasonic waves are used in sonography for the mapping of body organs. The Ultrasonic waves that are sent inside the body are reflected from the different parts by creating the echo. They are more useful and less harmful than radiation.


A microwave and an ultrasonic sound wave have the same wavelength. Their frequencies are in the ratio (approximately) 

physics range of hearing sound: production of sound audible, infrasonic and ultrasonic sounds different sounds

  1. $10^2$

  2. $10^4$

  3. $10^6$

  4. $10^8$

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Correct Option: C
Explanation:

Frequency of microwaves, $\upsilon _m \approx 10^{11}Hz$
Frequency of ultrasonic sound waves,$\upsilon _m \approx 10^5Hz$
$\therefore \, \dfrac{\upsilon _m}{\upsilon _u} = \dfrac{10^{11}}{10^{5}} = 10^6$

Which one of the following animals can hear infrasound?

physics range of hearing sound: production of sound audible, infrasonic and ultrasonic sounds different sounds

  1. rhinoceros

  2. bat

  3. dog

  4. honey bee

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Correct Option: A
Explanation:

Answer is A.

Rhinos have extremely good ears, picking up infra-sound far deeper than the range of human hearing.
Rhinos, can hear down to a frequency of four hertz, whereas even a human baby, with entirely undamaged ears, can normally only pick up sounds as low as 20 hertz. Giraffes and elephants can also hear in this infra-sound range.