Physics

Types of Heat Transfer: Radiation

len Alfred Ajibola - Thu, 26th December, 2019 @ 17:24: PM

Topics in Physics

Derived Units: Similarities and Differences with Fundamental Units Gravity: Interesting 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 Motion and Speed Concept of Heat Transfer Concepts of Heat and Temperature Gravity: What is Gravity? Zeroth Law of Thermodynamics - Thermal Equilibrium Fundamental Quantities and Units in Physics


Academic Questions in Physics

Please check out our Test Your Knowledge page to see all Questions and Answers

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

  • A. True

  • B. False

Force is a quantity measured in _____.

  • A. Kilogram

  • B. Gravity

  • C. Incandescence

  • D. Meter per second square (ms-1)

  • E. Mole

  • F. Newton

Heat transfer indicates two systems of varying temperatures and will always be transferred from a region with lower temperature to another with higher temperature.

  • A. True

  • B. False

Heat can be created.

  • A. True

  • B. False

Temperature is defined as the measure or ability of an object or substance to transfer heat energy to another object or substance.

  • A. True

  • B. False

Which of the following statement is incorrect concerning gravity?

  • A. It is a natural force of attraction

  • B. The earth is spherical in shape and we don't fall off it due to gravity

  • C. The amount of gravity is the same all around the spherical earth

  • D. Earth's gravity affects the satellites

  • E. Gravity is affected by size and closeness of objects

  • F. In an ideal space environment, gravity is absent

If two bodies are in thermal equilibrium with another body, then they are also in equilibrium with each other.

The above statement is the _____ law of thermodynamics.

  • A. Zeroth

  • B. First

  • C. Second

  • D. Third

  • E. Fourth

  • F. Fifth

Which of the following is a derived unit?

  • A. Kelvin

  • B. Meter

  • C. Newton

  • D. Candela

  • E. Mole

  • F. Ampere

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Heat Transfer - Radiation:

The term radiate in English mean to “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.

Note: 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. (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.

Note: 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.

All objects (televisions, phones, phones, computer and any other object) 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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Alfred Ajibola is a Medical Biochemist, a passionate Academician with over 7 years of experience, a Versatile Writer, a Web Developer, a Cisco Certified Network Associate and a Cisco CyberOps Associate.


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Amazing facts in Physics

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

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 actually 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.

Please read on gravity here

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.

Please read on motion, speed, velocity and acceeration here


NOTABLE POINTS IN Physics

The earth is governed by the force of gravity and that’s why everything present on it (humans, plants, animals and even air) is always drawn towards it. You will actually need some form of force greater than gravity in order to pull yourself away from the earth.

As an instance, the earth as we know is spherical in shape and held in space. Also, all humans live on a constantly rotating earth and not inside the earth. Since we live on a spherical earth held in space, how come humans are yet to fall off the constantly rotating earth?

Well, the answer is gravity. Even if we attempt to jump off the earth into space, the force of gravity present on earth will still pull us down. In fact, in order to leave the earth; there has to be a force stronger that gravity; which must be applied to whatever is attempting to leave the earth. For this reason:

Whenever one jumps, a certain amount of force is needed to be applied by that person. However, gravity still return the person back to earth because the applied force had been exhausted.

Please read more on the concept of gravity here.

The larger the size of an object, the greater it’s force of gravity. Gravity is therefore affected by the size and closeness of objects.

Since the earth is larger than the moon, it will have a greater gravitational force than the moon. We will be more attracted on the earth than we would on the moon if we were astronauts on the moon. This implies that we will weigh differently on both places. For this reason, our weight will also vary on the various planets (because they are of different sizes). This is shown in the diagram below:

Weights on planets - Len Academy

Weight depends on the degree at which the gravity on earth or moon or another planet pulls an object while the Mass of any object or body will always remain the same (constant) since it’s the amount or quantity of matter in the body.

Please read on Mass versus Weight here

Zeroth Law - Len Academy

To better understand what the Zeroth Law of Thermodynamics meant, we need to know what thermal equilibrium is. This is explained below:

Two bodies A and B are said to be in thermal equilibrium if each body can transfer heat to each other when placed closed together but ended up not transferring any heat to each other.

This will mean that both bodies are at equal temperature.

Now, according to the zeroth law, assuming we have three bodies namely X, Y and Z:

If X = Y and Z = Y, then X = Z

From the above expression, it will be observed that: if X and Y are in thermal equilibrium and Z and Y are in thermal equilibrium, therefore, X and Z must be in thermal equilibrium too.

So we can see that according to the zeroth law, temperature is a quantity worth measuring.

It can therefore be said that temperature is the quantity that remains constant (the same) for all systems in thermal equilibrium.

Consequently, the Zeroth Law of Thermodynamics states that if two separate bodies are in thermal equilibrium with another body, then they are also in equilibrium with each other

Please read more on the Zeroth Law of Thermodynamics here

Fundamental units are the units of fundamental quantities.

A fundamental unit is a unit that does not depend on any other unit; neither can it be changed nor is related to another fundamental unit.

Note: A fundamental unit is also referred to as a basic unit.

Fundamental Units are always constant. This means that they don't change, (remains the same) and are standardized all over the world.

The fundamental quantities alongside their respective fundamental unit are 7 in number. They include:

  1. Mass (m) is a fundamental quantity whose unit is kilogram (kg)

  2. Length (l) is a fundamental quantity whose unit is meter, (m)

  3. Time (t) is a fundamental quantity whose unit is second (s)

  4. Temperature (T) is a fundamental quantity whose unit is Kelvin (k)
    You can read on the Concept of Temperature and Heat here.

  5. Electric Current (I) is a fundamental quantity whose unit is ampere (A)

  6. Amount of Substance (n) is a fundamental quantity whose unit is mole (mol)

  7. Luminous Intensity (|v) is a fundamental quantity whose unit is candela (cd)

Please read more on fundamental units here

The Classical Mechanics (Laws of Motion) is a fundamental part of Physics.

Below are the Newton's Laws of Motion:

An object at rest will continue in its state of rest; while an object in uniform motion will continue in a straight line, unless an external force acts on it.

Newton's First Law of Motion.

Please read on Motion and Speed here.

The rate of change of momemtum is proportional to the applied force and will take place in the direction of that force.

Newton's Second Law of Motion.

To every action, there is an equal and opposite reaction.

Newton's Third Law of Motion.

Please read on Newton's Laws of Motion here.