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# Category Archives: Electromagnetism

## Transformers

Please explain what is transformer and tell what is the reason behind the working of transformer that it reduces potenial when current is high and increases potential when current is low?

Explain widely and deeply with concepts.

Transformer is a device based on mutual inductance and is used to change the voltage of alternating (or varying) current. There are two types of transformers – stepup and stepdown.

A step-up transformer increases the voltage as the step-down transformer decreases the ac voltage.

When a transformer changes the alternating voltage, it is not adding any power, it only transforms the voltage.

As power is the product of voltage and current, as voltage increases, the current decreases. (and vice versa)

## Force on a current carrying conductor in a magnetic field

Why the force acting on current carrying conductor when placed in a magnetic field increases with the increase in the current.?

I mean what happens inside it at that time? Please explain it in detail, it’s really confusing me, Please answer it as sson as possible.

Let’s consider the terms involved here first.

• Electric Current is the rate of flow of charges. An increase in current through a conductor means more number of electrons are crossing any cross section of the wire per second.
• A moving charge experience a force in magnetic field because a moving charge creates a magnetic field around it. The two interacting magnetic fields causes the force.

So, let’s summarize, when there is a current flowing through a conductor placed in a magnetic field, it experiences a force due to the mutual interaction between the magnetic fields – the already existing field and the field produced by the motion of current carriers (free electrons) inside the conductor.

When there is an increase in current, the force of interaction also increase as the numbers of free electrons flowing through any cross section also increases.

## How does a battery create potential difference?

How battery creates potential difference??? …plz give me a detailed description of it.

Posted by Arti.

Potential difference means “Difference in electrical potential. In an electrochemical cell, the potential difference is created by chemical reactions. In a cell there are two electrodes and they are maintained at different potentials by the chemical reactions taking place.

## Doubts from Electromagnetism

Let us suppose we have a loop of wire with some definite resistance in a magnetic field. Let the magnetic field be varying. This varying magnetic field will st up an EMF in the wire. My questions are as follows:

1). Energy is dissipated across the wire resistance. Where does this energy come from?

2). The current generated will also generate a varying magnetic field. Will this magnetic field generate another EMF in the loop? Will this go indefinitely?

## Doubts from Faraday’s Experiments on electromagnetic induction

I wanna ask that in faradays’s first experiment with coil and magnet,when the magnet is moved away from coil the deflection in galvanometer becomes opposite as compared to first case…..what leads to this and if that means direction of current becomes opposite so HOW and WHY the direction of this changes…..plz can you tell me the practical reason of this…..its really confusing me!!!

(Visitors are welcome to post their response via comments)

## WORKING OF A TRANSFORMER

Sir,im not understanding how transformer works?while current is going from one station to other we keep high voltage and very less current to decrease power loss but current is proportional to voltage how can u make low current using high voltage?

A transformer works on the principle of mutual induction. [mutual induction is the phenomenon of production of emf in a coil due to the change in the strength of current through a neighbouring coil]

Transformers are of two kinds – step up and step down.

A step up transformer converts low voltage (high current) ac to high voltage (low current) ac.

In the case of an ideal transformer, there is no power loss.

In that case,

input power = out power

Vin Iin = Vout Iout

[This equation shows how an increase in output voltage results in a decrease in out put current]

Long distance transmission of ac requires low  current as the heat dissipated during transmission is proportional to the square of current.

If we use a step-up transformer , it steps up the voltage and consequently steps down the current so that VI is the same.

In the case of real transformers, there are some power losses within the transformner, however, an increase in output current through mutual induction will essentially result in a decrease in output current.

Hope that the matter is clear now. In case of doubt, please post them as comments to this post.

## How does a microwave oven work?

Now, microwave oven is so popular that majority of houses have one. Many use it mainly to reheat food without loss of nutrient. The advantage is that the microwave heats up the food very fast.

Some observations made on microwave oven are,

• It does not heat up the vessels directly
• It is not able to cook food contained inside metal vessels
• If the turn table does not work, cooking will not be even.

So, it is pertinent to ask how the mechanism of heating in a microwave oven is different from other heating devices?

Here the water molecules, which are polar in nature play the magic. (A polar molecule is one in which the centre of mass of positive charges and the centre of mass of negative charges do not coincide and have a net dipole moment.) When microwaves are passed through food materials, the water molecules contained in them tends to turn and this rapid churning of water molecules develops a lot of heat. The turn-table adds to the churning and randomization developing heat more rapidly.

The food materials contained in a closed metal vessel will not be heated up by the microwave oven as they do not allow microwaves to pass through them. The metals are opaque to microwaves.

Why the food materials heated using microwave dry up and become stiff when cool?

In a microwave oven, the water molecules are heated very fats that the water is converted readily into steam. If kept open, the steam will escape and the material will become hard when cooled due to the decrease in the water content.

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