Electric Measurement

Basically, electric measurement means measurement of current, voltage and resistance in a circuit.We have already discussed that a voltmeter is used for measuring current. Both of these instruments work on ohm's law. The fundamental law in current electricity. Certainly, we did not discuss about the measurement of resistance. The instrument to the a resistance is called ohmmeter. An ohmmeter ,in fact, is a combination of a voltmeter and ammeter. It is important to note that all of these electrical instruments use energy from the source of electricity of which they are doing the measurement. It is, therefore, there fore, the measurements taken by them are slightly different from the actual measurements . In other words, some accuracy of measurement is lost with these instrument.
Hence , if we need move accuracy in the electrical measurement,we use potentiometer and Wheatstone bridge for the measurement of electricity. These devices use elaborate circuits for the measurement. However, these devices are much more accurate them the other.
In this sub-unit,we discuss in detail the principle and applications of accurate electrical devices.

Transfer of heat

Heat is a form of energy. Heat energy can be transfered from one place to another. Now , we talk about the mechaniisms of transfer of heat by conduction method. Conduction is one of the mechanisms of heat transfer. This takes place usually in solids. When ther exists temperature difference betwwen two points in solid, transfer of heat akes place from the point at high temperature to the point at low temperature without transferring the mass. This kind of transfer heat without transfer of mass is called heat conduction.

Heat conduction in solids can be explained the basis of kinetic theory of matter.A solid is made of a number of atoms which are fixed at lattice sites and are capable of vibrating about their mean positions.the amplitude of vibration of yhese atoms increases with the increase of temperature of solid.

Suppose that one end of a solid of bar is heated. The temperature if that end increases and the atoms in that region to vibrate with higher amplitudes due ro gain of thermal of heat energy. As a result, they collide with neighbouring atoms in cooler region . During such collision hot atoms transfer thermal energy to tje cold atoms and these atom also will begin to vibrate with higher amplitude. In turn, these neighbouring atoms collide with nextneighbouring vold atoms and so on. Thus, there will be continous transfer of heat thermal of thermal energy towards cold end. Here,heat is transfered from one atom to the other while each atom remaons vibrating about their original positions.

In matals there are many free electrons. The electrions are very small and can travel rapidly. When a bmetal is heated,their vibration increase and the energy is passed on to pther atoms and also the numerous electrons in the metal. The electrons rapidly transfer energy by collision to other electrons and other atoms. Hence the transfer of energy n metals is rapid.In non-metallic solids,there are very few free electrions.Here the only way that hewat can transfer through the solids is by direct transfer of energy from one atom another.Hence,yhe the transfer process slow.

Effects of Refraction of Light: Definition, Examples, Applications, and Everyday Phenomena

What is Refraction of Light?

Refraction of light is the bending or change in the direction of light when it passes from one transparent medium to another due to a change in its speed.

Light travels at different speeds in different media. When it moves from one medium to another-such as from air to water or from air to glass-its speed changes, causing the light ray to bend.

Definition:

Refraction of light is the change in the direction of light as it passes from one transparent medium to another because of a change in its speed.

Effects of Refraction of Light

Refraction produces several interesting optical effects that we observe in our daily lives. Some of the most common effects are discussed below. 

1. A Swimming Pool Appears Shallower Than It Actually Is

One of the most familiar effects of refraction is that a clear swimming pool or pond appears shallower than its actual depth.

Why does this happen?

Light rays coming from the bottom of the pool travel from water (denser medium) into air (rarer medium). As the rays emerge from the water, they bend away from the normal.

Our brain assumes that light travels in a straight line. Therefore, the bottom of the pool appears to be at a higher position than it actually is.

Result

• Apparent depth is less than the real depth.
• The pool appears shallower.

2. A Coin in Water Appears Raised

If a coin is placed at the bottom of a transparent container filled with water, it appears to be lifted upward.

Explanation

The light reflected from the coin bends away from the normal when it passes from water into air.

As a result, the eye sees the image of the coin at a position above its actual location.

Observation

• Actual position → Lower
• Apparent position → Higher

This is why the coin seems raised.

3. A Stick Partially Immersed in Water Appears Bent

A straight stick placed partly in water appears bent or broken at the water surface.

Reason

The portion of the stick inside water is viewed through refracted light rays.

Since the submerged part appears raised while the part above water remains unchanged, the stick appears bent at the interface between air and water.

This is one of the easiest demonstrations of refraction.

4. The Sun Appears Flattened During Sunrise and Sunset

During sunrise and sunset, the Sun often appears slightly flattened instead of perfectly circular.

Why does this happen?

The Earth's atmosphere consists of many layers of air with different densities.

• Air near the Earth's surface is denser.
• Air higher in the atmosphere is less dense.

As sunlight travels through these layers, it undergoes continuous atmospheric refraction.

The lower part of the Sun is refracted more than the upper part because its light passes through denser layers of the atmosphere.

As a result:

• The lower edge appears raised more than the upper edge.
• The vertical diameter appears shorter.
• The horizontal diameter remains nearly unchanged.

Therefore, the Sun appears flattened near the horizon.

5. Stars Twinkle at Night

he twinkling of stars is another beautiful consequence of atmospheric refraction.

Explanation

The Earth's atmosphere is made up of layers of air with continuously changing temperatures and densities.

As starlight passes through these layers:

• The amount of refraction changes continuously.
• The apparent position of the star shifts slightly from moment to moment.
• The intensity of light reaching our eyes also fluctuates.

This continuous change makes stars appear to twinkle.

Why don't planets twinkle as much?

Planets appear as small discs rather than point sources of light. The light from different parts of the disc averages out the fluctuations caused by atmospheric refraction, making planets appear steadier than stars.

Atmospheric Refraction

Atmospheric refraction is the bending of light as it passes through different layers of the Earth's atmosphere.

It is responsible for several natural phenomena, including:

• Twinkling of stars
• Flattened Sun at sunrise and sunset
• Advanced sunrise
• Delayed sunset
• Apparent shifting of celestial objects

Everyday Applications of Refraction

Refraction is used in many scientific instruments and technologies.

Application	Use of Refraction
Spectacles	Correct vision defects
Camera lenses	Produce clear images
Magnifying glass	Enlarges objects
Microscopes	Observe tiny objects
Telescopes	Observe distant celestial bodies
Binoculars	Magnify distant objects
Fiber optic communication	Transmit light signals efficiently

Summary of the Effects of Refraction

Effect	Cause
Swimming pool appears shallow	Bottom appears raised due to refraction
Coin appears raised	Image forms above the real coin
Stick appears bent	Submerged part appears shifted upward
Sun appears flattened	Unequal atmospheric refraction
Stars twinkle	Continuous atmospheric refraction

Frequently Asked Questions (FAQs)

What is refraction of light?

Refraction is the bending of light when it passes from one transparent medium to another because its speed changes.

Why does water appear shallower?

Light from the bottom of the water bends away from the normal as it enters the air, making the bottom appear raised.

Why does a stick look bent in water?

The submerged part appears higher than its actual position due to refraction, making the stick seem bent.

Why does the Sun appear flattened during sunrise and sunset?

The lower part of the Sun is refracted more than the upper part because the lower rays pass through denser atmospheric layers. This compresses the Sun's vertical diameter.

Why do stars twinkle but planets usually do not?

Stars are point sources of light, so atmospheric refraction causes noticeable fluctuations in their apparent brightness and position. Planets appear as small discs, and these fluctuations average out, making them appear steadier.

Conclusion

Refraction of light is a fundamental optical phenomenon that affects many aspects of our daily lives and our observations of the natural world. It explains why swimming pools appear shallower, coins in water seem raised, sticks look bent, the Sun appears flattened at sunrise and sunset, and stars twinkle in the night sky. Beyond these everyday observations, refraction is the working principle behind essential optical devices such as cameras, microscopes, telescopes, spectacles, and fiber-optic communication systems. Understanding the effects of refraction helps us appreciate both the beauty of nature and the science behind modern optical technology.