Advertisements
Advertisements
Question
Give a scientific reason.
Tungsten metal is used to make a solenoid type coil in an electric bulb.
Advertisements
Solution 1
- The electric bulb operates under the principle of the heating effect of electric current.
- The bulb’s solenoid-type coil has a very high melting point and high resistance.
- The solenoid-type coil of the lightbulb becomes heated to a high temperature (up to 3400°C) and begins to shine when current is delivered through it.
As a result, tungsten metal creates a solenoid-type coil in an electric bulb.
Solution 2
- The temperature of a bulb’s filament determines how much light it emits. It rises as the temperature does.
- The material used to construct a lightbulb's filament should have a very high melting point so that it can be heated to a high temperature by running a current through it without melting. We are able to get more light as a result. Tungsten has an extremely high melting point. It is possible to heat tungsten wire to around 3400°C.
Hence, tungsten is used to make a solenoid type coil (filament) in an electric bulb.
APPEARS IN
RELATED QUESTIONS
Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V.
An electric heater of resistance 8 Ω draws 15 A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater.
Why is the tungsten used almost exclusively for filament of electric lamps?
The safety device based on the heating effect of electric current is called a ______.
Write Joule's law of heating.
An electric heater is connected to the 230 V mains supply. A current of 8 A flows through the heater.
(a) How much charge flows around the circuit each second?
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
Which electric heating device in your home do you think have resistors which control the flow of electricity?
Give Scientific reason
In the electric equipment producing heat e.g. iron, electric heater, boiler, toaster etc, an alloy such as Nichrome is used, not pure metals.
Identify the figure and give its use.
Heat energy is being produced in a resistance in a circuit at the rate of 100 W. The current of 3 A is flowing in the circuit. What must be the value of the resistance?
Solve the following example.
Two tungsten bulbs of wattage 100 W and 60 W power work on 220 V potential difference. If they are connected in parallel, how much current will flow in the main conductor?
Statement 1 : Electric current ( flow of electrons ) creates heat in the resistor.
Statement 2 : Heat in the resistor is created according to the rule of energy conservation.
Explain Statement 1 with the help of Statement 2.
Write the mathematical expression for Joule’s law of heating.
What is overloading?
Name any two appliances which works on the phenomenon of heating effect of electric current.
When does overloading occur?
Define fuse.
Name some devices that run using heat effect of electric current
Mark the correct choice
- Assertion: Electric appliances with a metallic body have three wire connections.
- Reason: Three-pin connections reduce the heating of the connecting wires.
An electric iron draws a current of 4 A when connected to 220 V mains. Its resistance must be:
A current of 1 A is drawn by a filament of an electric bulb. Number of electrons passing through a cross-section of the filament in 16 seconds would be roughly:
B1, B2 and B3 are three identical bulbs connected as shown in Figure. When all the three bulbs glow, a current of 3A is recorded by the ammeter A.
- What happens to the glow of the other two bulbs when the bulb B1 gets fused?
- What happens to the reading of A1, A2, A3 and A when the bulb B2 gets fused?
- How much power is dissipated in the circuit when all the three bulbs glow together?
Three incandescent bulbs of 100 W each are connected in series in an electric circuit. In another circuit another set of three bulbs of the same wattage are connected in parallel to the same source.
- Will the bulb in the two circuits glow with the same brightness? Justify your answer.
- Now let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason.
(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).
Unscramble the following words:
SFEU
Your teacher has shown you the following activity.
Activity: Teacher has wound a long insulated piece of wire around an iron nail in the form of a coil. Free ends of the wire are connected to a cell through a switch as shown in the following figure. The current is switched on and some pins are placed near the ends of the nail.
Write down any three questions that come to your mind about this activity.
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 is an electric fuse made up of?
What are the factors affecting heating effect of electric current?
Copper wire offers very little ______ and does not get heated up quickly.
Name a few appliances which work on the basis of the heating effect of current.
A student boils water in an electric kettle for 20 minutes. Using the same mains supply he wants to reduce the boiling time of water. To do so should he increase or decrease the length of the heating element? Justify your answer.
The following is not a safety device.
State the law that explains the heating effect of current with respect to the measurable properties in an electrical circuit.
When a current I flows through a wire of resistance R for time t then the electrical energy produced is given by ______.
