Physics

Types of Heat Transfer: Radiation

len Alfred Ajibola - Thu, 26th December, 2019 @ 5:24 PM

Topics in Physics

Derived Units: Similarities and differences with fundamental units Gravity: Facts on Gravity Relative Density of Substances and Specific Gravity Types of Heat Transfer: Conduction Types of Heat Transfer: Convection Types of Heat Transfer: Radiation Physics Scheme of Work, SS1, First Term Physics Scheme of Work, SS1, Second Term Physics Scheme of Work, SS1, Third Term Velocity and Acceleration Newton's Laws of Motion Importance of Gravity What is Density? Density of various substances Concepts of Force and Motion in Physics Motion and Speed in Physics Concept of Heat Transfer Concepts of Heat and Temperature What is gravity? Concept of gravity on the solar system Zeroth Law of Thermodynamics: Thermal Equilibrium Fundamental Quantities and Units in Physics


Academic Questions in Physics

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Which of the following is a fundamental quantity?

  • A. Luminous Intensity

  • B. Area

  • C. Volume

  • D. Velocity

  • E. Concentration

  • F. Acceleration

An object at rest will temporarily stay in its state of rest, and if the object is in uniform motion, it will temporarily move in a straight line, unless an external force acts upon it.

The above statement refers to Sir Isaac Newton's first law of motion.

  • A. True

  • B. False

Which of the following statement is incorrect concerning gravity?

  • A. The force of gravity is generally considered the strongest force among the four forces that govern the universe

  • B. Your weight changes as you travel away from the earth

  • C. If we dig the earth until we get into its center, we will have no weight as a result of lack of gravity

  • D. Gravity prevents us from falling off the constantly rotating earth

  • E. If a hammer and a feather are dropped simultaneously in a vacuum, they will both land at the exact same time as a result of gravity

  • F. Weight is always a function of gravity

Isaac Newton Hit by Apple - Len Academy

Sir Isaac Newton was hit by an apple when he pondered on force, motion and gravity.

  • A. True

  • B. False

The movement of gaseous particles through a tiny hole is termed _____.

  • A. Osmosis

  • B. Diffusion

  • C. Effusion

  • D. Infusion

  • E. Defusion

  • F. Gaslusion

A lighted bulb transfers heat through a process termed _____.

  • A. Conduction

  • B. Convection

  • C. Radiation

  • D. Oxidation

  • E. Reduction

  • F. Electrical Induction

A measurement of how much the velocity of an object changes with time is termed _____.

  • A. Displacement

  • B. Acceleration

  • C. Speed

  • D. Momentum

  • E. Velocity-Time graph

  • F. Average velocity

Which of the following differentiates velocity from speed?

  • A. Distance

  • B. Time

  • C. Momentum

  • D. Inertia

  • E. Direction

  • F. Distance and Time



Heat Transfer - Radiation:

The term 'radiate' in English means to spread out from a central point. For instance, the light from the sun radiates to the earth. Also, a lighted bulb will radiate its light in a dark room.

The term radiation (heat radiation) can simply be defined as the transfer of heat in the form of electromagnetic waves.

Please read on heat transfer through convection here.


Whenever heat is transferred via radiation, a contact surface will not be required between the heat source and the object being heated. In this case, the heat is transmitted through space.

One reason why some people put out their bulbs before they go out is to simply conserve energy. Leaving on the bulb will bring an extra heat into the room where it’s present.

Please read on the concept of heat and temperature here.


Consider the points below regarding radiation through a lighted bulb:

  • A bulb will possess a large amount of heat energy if left switched on for a long period of time. Meanwhile, recall that a bulb converts electrical energy to light and heat energy.
  • Since energy cannot be lost, the heat energy from the bulb will be radiated around the room where it’s present. The energy transfer goes thus:
Electrical Energy >> Light Energy >> Heat Energy

This process of heat transfer from the bulb to the room is a concept of radiation.

Please read on the concept of heat transfer here.


In radiation, the heat energy is transferred by electromagnetic waves. In fact, the heat energy which the earth receives from the sun is as a result of electromagnetic waves travelling through space.

Please read on heat transfer through conduction here.


The image below shows how heat is radiated to earth from the sun's solar energy:

Heat Transfer by Radiation - Len Academy

Please read on the solar system here.


Electronic objects, for example: televisions, phones, computer and cars will always radiate energy in the form of electromagnetic waves. The rate at which this energy is released is directly proportional to the Kelvin temperature (T) raised to the fourth power.

Radiation rate = k•T4


The hotter an object is, the more its ability to radiate heat energy. The radiated energy is a collection of a range of wavelength referred to as emission spectrum.

The wavelengths within the spectra of the emitted radiation will decrease when the temperature of an object increases; and as a result, hotter objects will usually emit a shorter wavelength at a higher frequency.

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Amazing facts in Physics

Marie Curie was the first person ever to win two Nobel prizes. She won her first Nobel price for physics in 1903, and the second for chemistry in 1911 for her work on radioactivity.

The hottest temperature ever recorded occurred in Furnace Creek Ranch, Death Valley, California, USA, at 56.7oor (134oF) on July 10, 1913

Elephant on cumulus cloud - Len Academy

A medium-sized cumulus cloud has a weight of about 80 adult elephants.

You can think of cumulus cloud as a detached, individual, cauliflower-shaped cloud often seen in fair weather conditions

Leaning Tower of Pisa - Len Academy

The reason the Leaning Tower of Pisa is tilted is the same reason it's still standing

One quarter of an apple is filled with air and that's why they float in water

Alfred Noble - Len Academy

The Nobel price was named after its founder, Alfred Noble. He is a Swedish, born on October 21, 1833; and was the inventor of dynamite. He was also a a famous scientist and a successful business man.

Glass Ball - Len Academy

Glass balls bounce higher than rubber balls

Every planet has its own unique gravitational force. For instance, Mars has a gravity of 3.711 m/s2 while earth’s gravitational force is 9.807m/s2.

When two metals are put together in space, they will stick together as if they are welded. This phenomenon is called cold welding

The fastest animal on land is cheetah. It can reach a maximum speed of about 113km per hour.


Notable points in Physics

The Standard International (SI) unit for density is kilogram per cubic metre (Kg/m3).

The table below shows various substances with their densities:

Substance

Density (Kg/m3)

Helium

0.179

Air (1atm and 20oC)

1.20

Bamboo Wood

400

 Ethanol

810

Methylated Spirit

800

Benzene

900

Paraffin Wax

900

Ice

920

Water (Fresh Water)

1000


Please read on density here

Force can be balanced or unbalanced.

When forces from different directions act on an object and consequently bring about the object's motion, then such forces are unbalanced.

Conversely, if theses forces bring about zero motion (static position or no movement) on the object of reference, then it's a balanced force.

In summary,

  • An apple hanging on a tree (without any form of movement) has a balanced force.

  • An apple falling from a tree has an unbalanced force.

If one covers a distance of 10,000 meters in 50 seconds and another covers the same distance in 5,000 seconds, we can conclude that the first person has a greater speed because he covered the same distance at a lesser time.

  • Speed is defined as distance travelled per unit of time. It can also be defined as the rate of change of distance.

Speed = distance/Time

Speed is a scalar quantity since it has only magnitude. Speed does not have a direction.

In physics, motion is defined as a change in the position of an object with reference to time.

Although we sometimes sit or stand in a fixed position, that doesn’t mean motion isn’t taking place. The fact that the earth is constantly rotating implies that we are indirectly moving along with it. We can thus say that motion can be relative to some frame of reference.

In the above paragraph, the earth (constantly rotating along its axis) is our frame of reference and everything present on earth is in motion (with regard to earth as a frame of reference).

Please read on the concepts of motion and speed here

Heat is a form of energy. It cannot be lost according to the first law of Thermodynamics; rather it will be transferred. The first and second laws of thermodynamics are stated below:

  • Energy can neither be created nor destroyed but can be transformed or converted from one form to another.

    1st law of thermodynamics


  • In the course of energy transfer, some energy is lost in the form of heat to the surroundings.

    2nd law of Thermodynamics

Please read on the concept of heat transfer here