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## What are the similarities and differences in magnetic and electric field?

Similarities and differences in magnetic and electric field (Dilpreet posted this question)

 Similarities Differences Both electric and magnetic field are conservative forcesBoth obey inverse square law Both are non contact forces (Forces can be exerted without contact) Both are attractive as well as repulsive (Like poles repel, like charges repel; unlike poles attract, unlike charges attract) Electric field is produced by a charge whether at rest or in motionBut magnetic field is produced only by a moving charge   The total magnetic flux through any closed surface is always zero, but the total electric flux through any closed surface is equal to the net charge enclosed by the surface multiplied by the reciprocal of absolute permitivity Electric field lines are discontinuous as they have a starting point (+ charge) and an ending point (- charge); But magnetic field lines are continuous, they always form closed loops

## Gravitation – Questionbank with answer for CBSE Class 9 SA1

The following questions are for a quick revision of the chapter “Gravitation” for CBSE Class 9. There are many other questions which can be asked from the portion allotted for SA1, but will mainly based on these concepts. The questions are based on the bare essential concepts; the minimum level of learning expected from the children

1. State the universal law of gravitation.
Universal law of gravitation states that every object in the universe attracts every other object with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them
2. Define G. Write its value with proper units of SI
G is the universal constant of gravitation. It is defined as the gravitational force of attraction between two objects of mass 1 kg each separated by a distance of 1m. Its value is 6.67 x 10-11 Nm2kg-2
3. What is the difference between gravity and gravitation?
The force of gravitation exerted by earth (or any other planet) on the objects on its surface is called gravity. Every object attracts every other object due to the force of gravitation. So, Gravity is a special case of Gravitation
4. Define acceleration due to gravity.
5. Why the moon is not “falling” to earth?
6. Derive an expression for the acceleration due to gravity.
7. Write the differences between g and G.
8. calculate the value of g on the surface of earth.
9. Discuss the variation of g with height, depth and latitude.
10. Distinguish mass and weight.

## Variation of acceleration due to gravity with depth. A doubt.

Rajkumar asks: “accelaration due to gravity decrease on depth of earth with the relation of g’=g(1-2h/R). but with relation of g=GM/(R*R)  g increase.

Answer:

When the object is on the surface or above it, the entire mass of the earth attracts it. But when it is inside, the net attraction towards CENTRE is provided only by the mass of earth below it. ie; if it is at a depth d below the surface, then it is attracted to the centre by a sphere of radius R-d only. The forces due to the rest of the mass of earth cancel out. (On one side there is a little mass and on the other side greater amount of mass but distributed faraway and both contribute equally towards force and cancel out.)

## Coulombian force and conductor

what’s effect of  coulombic forces on conductor medium ?

amk niazi

Ans:

In a conductor, the coulombian  repulsive forces  pushes the valence electrons and the electrons move away from the center to the surface ie from the region of stronger force to the region of lesser force, creating a Faraday cage

## Acceleration due to gravity

Does the acceleration due to gravity remains constant within the earth’s atmosphere or does it keep decreasing as we go up from the earth’s surface?

Rashshad Rasheed

Answer

No acceleration due to gravity decreases as we go up from the earth’s surfacs

## Variation of acceleration due to gravity with height

I want to ask that does the acceleration due to gravity remains constant within the earth’s atmosphere or does it keep decreasing as we go up from the earth’s surface?

Rashshad Rasheed asked

## Define area vector in simpler terms Area vector is a vector whose magnitude is equal to the area and is directed normal to the surface.

Area as such is a scalar. So, Area vector is defined as above for use in calculations and defining some other terms like torque on a current carrying loop in a magnetic field etc.

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