Advertisements
Advertisements
प्रश्न
What is Joule’s heating effect? How can it be demonstrated experimentally? List its four applications in daily life.
Advertisements
उत्तर
Joule's law of heating states that heat produced in the resistor is
- directly proportional to the square of the current.
- directly proportional to the resistance.
- directly proportional to the current.
Mathematically,
H = i2Rt
where,
H = Heat produced
I = Current
R = Resistance
t = time
Experimental demonstration
- Take a water heating immersion rod, water, bucket, thermometer, regulator.
- Immerse the water heating immersion rod in the water and measure the time taken to heat the water upto a certain temperature.
- Now increase the current to double with the help of regulator and now measure the time taken to heat the water upto the same temperature.
Then, we will observe that time taken in second case will be one fourth the time taken in earlier case. Hence, it verifies the Joule's law of heating.
Electric fuse, toaster, oven, kettle, are the four applications of Joule's law of heating in daily life.
APPEARS IN
संबंधित प्रश्न
Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?
What is nichrome? State its one use.
Give two reasons why nichrome alloy is used for making the heating elements of electrical appliances.
Why are the coils of electric irons and electric toasters made of an alloy rather than a pure metal?
An electric kettle rated at 220 V, 2.2 kW, works for 3 hours. Find the energy consumed and the current drawn.
Explain why, the current that makes the heater element very hot, only slightly warms the connecting wires leading to the heater.
Which of the following characteristic is not suitable for a fuse wire?
(a) thin and short
(b) thick and short
(c) low melting point
(d) higher resistance than rest of wiring
The electrical resistivities of four materials P, Q, R and S are given below:
| P | `6.84xx10^8`Ωm |
| Q | `1.70xx10^8`Ωm |
| R | ` 1.0xx10^15`Ωm |
| s | `11.0xx10^-7`Ωm |
Which material will you use for making: (a) heating element of electric iron (b) connecting wires of electric iron (c) covering of connecting wires? Give reason for your choice in each case.
Two exactly similar heating resistances are connected (i) in series, and (ii) in parallel, in two different circuits, one by one. If the same current is passed through both the combinations, is more heat obtained per minute when they are connected in series or when they are connected in parallel? Give reason for your answer.
Name any six domestic appliances based on the heating effect of electric current.
Find the odd one out and give its explanation.
True or False – If False give the correct answer
The fuse wire does not melts whenever there is overload in the wiring.
(a) Observe the diagram given below and state whether the bulb will glow or not when we switch on K.
(b) Is it safe to handle the bulb when the switch is OFF?
(c) Give a reason for your answer in (b).
Can we use the same fuse in a geyser and a television set? Explain.
Paheli took a wire of length 10 cm. Boojho took a wire of 5 cm of the same material and thickness. Both of them connected the wires as shown in the circuit given in the following figure. The current flowing in both the circuits is the same.
- Will the heat produced in both cases be equal? Explain.
- Will the heat produced be the same if the wires taken by them are of equal lengths but of different thickness? Explain.
What are the factors affecting heating effect of electric current?
Explain the working of an electric fuse.
Assertion: A current-carrying wire should be charged.
Reason: The current in a wire is due to the flow of free electrons in a definite direction.
In the electric equipment producing heat like iron, electric heater, boiler, toaster etc., an alloy such as nichrome is used, not pure metals.
In a set up the students coated iron nails with zinc metal and noted that, iron nails coated with zinc prevents rusting. They also observed that zinc initially acts as a physical barrier, but an extra advantage of using zinc is that it continues to prevent rusting even if the layer of zinc is damaged. Name this process of rust prevention and give any two other methods to prevent rusting.
