Tag: physics

Questions Related to physics

A $0.21\space H$ inductor and a $12\Omega$ resistance are connected in series to a $220\space V, 50\space Hz$ ac source. The current in the circuit is :

ac voltage applied to a series lr circuit lr circuit phase relations between alternating voltage and alternating current in different types of alternating current circuits and phasor diagram electromagnetic induction and alternating currents physics

  1. $\displaystyle\frac{220}{\sqrt{4400}}A$

  2. $\displaystyle\frac{22}{3\sqrt5}A$

  3. $\displaystyle\frac{220}{\sqrt{4550}}A$

  4. $\displaystyle\frac{22}{5\sqrt3}A$

Show answer
Correct Option: B
Explanation:

$ X _L = L 2 \pi f = 0.21 \times 314 \Omega $
$ R = 12 \Omega $
$ I = \dfrac{ 220}{ \sqrt{ X _L^2 + R^2 } } = 3.28 = \dfrac{22}{3\sqrt{5}} A  $

An A.C voltage $V=5\cos { \left( 1000t \right) V } $ is applied to a L-R series circuit of inductance $3mH$ and resistance $4\Omega$. The value of maximum current in the circuit is  _______ A

ac voltage applied to a series lr circuit lr circuit phase relations between alternating voltage and alternating current in different types of alternating current circuits and phasor diagram electromagnetic induction and alternating currents physics

  1. $0.8$

  2. $1.0$

  3. $\cfrac{5}{7}$

  4. $\cfrac { 5 }{ \sqrt { 7 } } $

Show answer
Correct Option: B
Explanation:

$V=5\cos { \left( 1000t \right) V } $

The standard equation for the voltage is:
$V={ V } _{ 0 }\cos { \omega t } $

So, from the equation, ${ V } _{ 0 }=5volt;\omega =1000rad/s$
$L=3\times { 10 }^{ -3 }H,R=4\Omega $

Maximum current $10=\cfrac { { V } _{ 0 } }{ Z } \quad $
$10=\cfrac { 5 }{ \sqrt { { \omega  }^{ 2 }{ L }^{ 2 }+{ R }^{ 2 } }  } =\cfrac { 5 }{ 5 } =1A\quad \quad $

The surface of the head of a match stick and sides of a match box are deliberately made rough to:

physics friction increasing and reducing friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it

  1. increase friction

  2. decrease friction

  3. increase amount of heat

  4. decrease amount of heat

Show answer
Correct Option: A
Explanation:

The rough surface will increase the friction and so the rough surface of match box and match stick will produce more friction which helps in firing the stick easily.  

Correct air pressure in our vehicle tyres help to reduce:

physics friction increasing and reducing friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it

  1. static friction

  2. sliding friction

  3. rolling friction

  4. all of the above

Show answer
Correct Option: C
Explanation:

Correct air pressure helps in reducing deformation of the tyre and also provide an air cushion to reduce rolling friction. 


Option C is correct.

Wheels reduce friction due to:

physics friction increasing and reducing friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it

  1. more area of contact

  2. less area of contact

  3. size

  4. all of the above

Show answer
Correct Option: B
Explanation:

The friction will be more for more area of contact. Since the wheels have less area of contact so the friction will be less for them. 

With increase of temperature, the frictional force acting between two surfaces increases.

physics friction increasing and reducing friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it

  1. True

  2. False

  3. Ambiguous

  4. Data Insufficient

Show answer
Correct Option: B
Explanation:

Friction decreases with increase in temperature.

Friction is minimised by using

physics friction increasing and reducing friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it

  1. Wheels and balI bearings

  2. More number of tyres in a car

  3. Rough surfaces

  4. None of these

Show answer
Correct Option: A
Explanation:

Answer is A.

Bearings reduce friction by providing smooth metal balls or rollers, and a smooth inner and outer metal surface for the balls to roll against. These balls or rollers 'bear' the load, allowing the device to spin smoothly.
The concept behind a bearing is very simple. Things roll better than they slide. The wheels on our car are like big bearings. If we had something like skis instead of wheels, our car would be a lot more difficult to push down the road.
That is because when things slide, the friction between them causes a force that tends to slow them down. But if the two surfaces can roll over each other, the friction is greatly reduced.

powder sprinkled on a carrom board

physics friction increasing and reducing friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it

  1. magnifies friction.

  2. reduces friction.

  3. removes friction.

  4. does not affect friction.

Show answer
Correct Option: B
Explanation:

The carom board may sometimes be very rough. Sprinkling powder on a microscopic level, the powder particles offer rolling friction to the striker because of which the striker can be used for smooth and fast play.

The force of friction on a static body ________ , if It is on a rough surface then.

physics friction increasing and reducing friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it

  1. is always zero

  2. may be gravity.

  3. may be zero

  4. both B & C

Show answer
Correct Option: D
Explanation:

The force of friction f is always opposite the direction the object that is moving . If the object would move, then the direction of the force of friction f will be opposite the movement. If the object would not move when there is no friction, then the force of friction is zero.Hence, though the surfaces of the object are rough the force of friction can be zero if the object would not move.

Powder is used in carrom board for

physics friction increasing and reducing friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it

  1. Increasing friction

  2. Decreasing friction

  3. Decoration

  4. Fragrance

Show answer
Correct Option: B
Explanation:

Answer is B.

The surface well powdered to stay away from harm to board surface due to scratch.It reduces the friction and helps in smoothing of the board and thereby allows the carom coins to go through in that flow which helps in fast play.
Powder is used in carom board for decreasing friction.