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In transverse wave,the particles vibrate perpendicular to the direction of wave propagation.

“light is a transverse wave.”
but light can be propagated without a medium , that is particles.
so, how can light be called as a transverse wave?


Light is an electromagnetic wave which requires no medium for the propagation. In electromagnetic waves including light, electric and magnetic fields vary with time in mutually perpendicular directions and also perpendicular to the direction of propagation.

Force on a charged particle

What is the force experienced by a charged particle moving perpendicular to an electric field? I understand that when it is moving parallel to the electric field, it accelerates.

(Shrishti asked)


When a charged particle is at rest in an electric field, it experiences a force in the direction of electric field (if it is a positive charge)

If it is moving in the direction of electric field, it will be accelerated.

If it is moving opposite to the electric field, it will be decelerated.

If it is moving perpendicular to the electric field, its trajectory will be a parabola, similar to that of a horizontal projectile

Restoring force and Newton’s law

We know that whenever a body is deformed a restoring force originates and tries to restore the shape of the body and according to newtons third law of motion whenever a force acts on a body an equal and opposite force acts on the other body . So is the restoring force an opposite reacton to the deforming force and if it is not then why do we consider its direction equal and opposite to the deforming force while solving problems .

(Asked Akshat )

Answer: Restoring force comes into play only when a deforming force is exerted. When no external force acts on a body, the molecules are in equilibrium. No net force acts on it. If an external force is applied on it, it will try to  increase or decrease the intermolecular distance giving rise to a state of inequilibrium to teh molecules and they will tend to go back to their original positions to retain their state of equilibrium. This gives rise to the RESTORING FORCE.

Restoring force the the internal force that comes into play whenever an external force tries to change the inter-molecular distance. The restoring force at any instant (within limits) is equal in magnitude and opposite in direction to the deforming force

What is the answer if vector A is multiplied with vector B?

In vector multiplication, there are two types of multiplication: One in which the result is a scalar and the other in which the result is a vector.

Accordingly the two types of products of vectors are:

Scalar product (also called dot product) denoted byA.B

Vector product (also called cross product) denoted by AxB

A.B  = AB cos Θ, where Θ is the angle between the directions of A and B

The physical meaning of dot product is that, “The product of the magnitude of one vector and the magnitude of the component of the other vector in the direction of the first vector.”

AxB = AB sinΘ \hat{n}

The direction of cross product is given by right hand cork screw rule

cross product

Motion of a charge particle in an electric field – Numerical Problem

At t=0 a very small object with mass 0.400mg and charge +9.00μC is travelling at 125 m/s in the -x-direction. The charge is moving in a uniform electric field that is in the +y-direction and that has magnitude E= 895 N/C. The gravitational force on the particle can be neglected. How far is the particle from the origin at t= 7.99 ms.

Hint for solving the above problem:

displacement along X direction; x=-uxt=125 x 7.99/1000

Displacement along Y direction, y=0.5 ay t2



Just substitute the values and get the answer

Why direct currents aren’t used in Home circuits?

How can an alternating current change its direction while moving in a wire or any conductor? Why direct currents aren’t used in Home circuits?



Alternating current is produced by rotating a coil in a strong magnetic field (or by rotating magnet around the coil)

So, during every half rotation the direction of emf (voltage) induced in the coil reverses and hence the current too reverses its direction. The frequency of ac in India is 50 Hz and therefore in every 1 sec there will be  100 changes in direction.

Alternating currents are suitable for long distance as it can be stepped up using transformer to minimize energy loss and can be stepped down for use at home.


More problems coming in; Try to answer now!

Stuti posted these:

  1. a particle is thrown with  any velocity vertically upward. the distance traveled by particle in last sec of ascent is 1)g 2)g/2 3)g/4 4)cant be calculated
  2. a ball is dropped from a bridge of 122.5 metre above a river. after ball has been falling for 2 sec,a second ball is thrown straight down after it. initial velocity of second ball so that both hit water at sme time is 1)49 m/s 2)55.5 m/s 3)26.1 m/s 4)9.8 m/s.
  3. two cars are moving in same direction with a speed of 30 km/hr. they are separated from each other by 5 km. third car moving in opposite direction meets the two cars after an interval of 4 minutes. the speed of third car is 1)30 km/hr 2)25 km/hr 3) 40 km/hr 4)45 km/hr
  4. a balloon starts rising from ground from rest with an upward acceleration 2 m/s^2. jst after 1 sec , a stone is dropped from it. time taken by stone to strike ground is nearly 1)0.3 sec 2)0.7 sec 3)1 sec 4)1.4 sec

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