Joule's law of Heating & Joules First Law
Joule’s Law of Heating explains how heat is produced when electric current flows through a conductor. As current passes through a wire, electrons collide with the atoms of the conductor, increasing its internal energy and producing heat. This heating effect of electric current is commonly observed in daily life, such as in electric irons, heaters, bulbs, and fuses. To study and measure the amount of heat produced during the flow of current, the English scientist James Prescott Joule proposed a simple mathematical law known as Joule’s Law of Heating. This law tells us how heat depends on current, resistance, and time. Understanding Joule’s Law is very important for Class 10 students, as it forms the basis of many electrical applications and numerical problems in physics.
This Story also Contains
- Joule’s Law of Heating
- Derivation of Joule's first law
- SI Unit in Joule’s Law of Heating
- Applications of Joule's Law
- Solved Examples of Joule's law
Joule’s Law of Heating
Joule's law of heating states that the heat produced in a conductor due to the flow of electric current is directly proportional to
1. the square of the current passing through it,
2. the resistance of the conductor, and
3. the time for which the current flows.
$
H=I^2 R t
$
where
- $H=$ heat produced,
- $I=$ current,
- $R=$ resistance ,
- $t=$ time .
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Derivation of Joule's first law
When a current $I$ flows through a resistor $R$, the work done in time $t$ is given by:
$
W=V I t
$
where $V$ is the potential difference.
Using Ohm's law $V=I R$, the work done becomes:
$
W=(I R) I t=I^2 R t
$
The work done by the current in the resistor is entirely converted into heat energy (neglecting other losses). Thus:
$
H=I^2 R t
$
SI Unit in Joule’s Law of Heating
According to Joule's law of heating,
$
H=I^2 R t
$
The SI unit of heat produced (H) is joule (J).
Applications of Joule's Law
- Electric heaters: Heat is generated in devices like room heaters and electric kettles.
- Fuses: Joule's law explains why fuses melt when excessive current flows through it.
- Electric Bulb: The filament glows due to the heat generated by electric current.
Solved Examples of Joule's law
Q1) Calculate the thermal energy produced to withstand $5 \Omega$ when the current 3 flows through it for 2 minutes.
Solution:
The temperature generated by the operator is given in the formula:
$
H=I^2 R t
$
$t=$ Time (in seconds) $=2$ minutes $=2 \times 60=120$ seconds
Substitute the values:
$
\begin{gathered}
H=(3)^2 \times 5 \times 120 \\
H=9 \times 5 \times 120=5400 \text { joules }
\end{gathered}
$
Q2) The $300 \Omega$ resistance heater is connected to the main feed for $\mathbf{3 0}$ minutes. If 10 current flows through a heater then what is the heat generated in the heater?
Solution:
The temperature generated by the heater is calculated as follows:
$\mathrm{H}=\mathrm{I}^2 \mathrm{RT}$
- $t=$ time ( 30 minutes $=30 \times 60=1800$ seconds)
Substitute the values
$
H=(10)^2 \times 300 \times 1800
$
$
H=100 \times 300 \times 1800=54,000,000 or 54 \mathrm{~MJ}
$
Frequently Asked Questions (FAQs)
When electrical energy passes through the conductor, it increases the internal energy of the system, which in turn increases the energy of the atomic net and its molecules, which in turn leads to heat production. The heat generated in the system mainly depends on the major factors, namely
Electrical resistance provided by the operator is more resistance; there will be more heat to be produced.
The more current it flows, the more time it has, the more heat it produces.
The current value exceeds the driver. The higher the current size; heat is highly generated.
1. Electric Heating Device
Other electrical appliances such as an electric heater, an electric toaster, and an electric heater are based on the current energy efficiency policy. In these applications, Nichrome (nickel alloy and chromium) is used as a heating element in many electrical devices. This is for the following reasons,
Nichrome has some high opposition.
Nichrome has a very melting point.
Nichrome is not easily integrated.
2. Fuse cable
Fuse cord is a mixture that contains 37% lead and 63% tin. Fuse cable is always connected to the series in the electrical circuit. With its high resistance to low melting point, when a large amount of electrical energy flows through the electrical circuit, the fuse wire melts, thus making the circuit open and preventing any damage to electrical equipment.
3. Electric Lamp
The power cord provides very high resistance to electrical flow, which is why a high temperature is produced. This cord, when intensified by incandescence, emits light. The most used cable is Tungsten, which has a high melting point of 3380 ° C.
Electric arc and electric heating are also based on the joule heating effect of current electric heating.
Joules law of electric heating does not help even when the concept is used in systems such as transformers and dynamos. These are devices that help reduce energy loss due to the heat joule heating effect of electrical energy.
Other energy heating applications are:
Water heater
Incandescent lamp (when its cord is heated produces light).
Fuse (fuse melts and stops the flow of comments now in the region, reducing damage to home devices)
Electrical metal
Electric stove.
Thermistors: Thermistors are a type of resistance to their resistance when changes occur.
Joule is a power unit of SI; it represents the amount of energy contained in the body. Watt is a measure of power conversion and is a unit of power SI.
Power = Time Power Time
Here unit Joule is equal to the value of a watt unit per second unit.
Watts = Joules / time
Energy is a measure of energy consumption per system.
1 Joule per second = 1 Watt
Joules law of temperature states that if the 'i' current passes through the resistor 'r' and the time 't' then the heat generated on the conductor is equal to the product of the square, the resistance at the same time.
Joules law, on electricity, is a mathematical definition of the rate at which circuit resistance converts electrical energy into thermal energy. ... You have found that the heat from a second equals the amount of electricity absorbed, or the loss of energy.
Joules law of temperature states that if the 'i' current passes through the resistor 'r' and time 't' then the heat generated in the conductor is equal to the product of the square square, the time resistance. H = i 2 rt.
James Prescott Joule
James Prescott Joule, (born December 24, 1818, at Salford, Lancashire [now Greater Manchester], England - died October 11, 1889, Sale, Cheshire), an English scientist who discovered that different forces - mechanical, electrical, and thermal - alike is the same and can be changed to something else.