Effects Of Electric Current

Nichrome is used as a heating coil because:

i. It has a high resistance and so a large amount of heat is produced on passing current through it.

(heat generated per second = current²× resistance)

ii. It has a high melting point and thus it can achieve a high temperature without getting destroyed (melting or getting burnt).

iii. It can remain in red hot condition for a long time without getting oxidised.

i. The ends of the fuse wire must be connected firmly.

ii. The fuse wire shouldn’t project out of the carrier base.

iii. The fuse wire should be of appropriate amperage, else it will not serve the purpose of protecting the user and the appliance from damage due to excessive flow of current.

Given:

Power = 920 W = 920 J/s

(∵ 1 Watt = 1Joule/sec)

Time = 5 mins = 5 × 60 seconds = 300 seconds.

Formula used:

Heat, H = Power × time

⇒ H = 920 J-sec^-1 × 300 sec

= 276000 J

= 276 × 10³ J

∴ 276 kilo joules energy will be generated in the heater when the current flows for 5 mins.

i. When the discharge lamp is connected to a source of electricity, the gas in between the electrodes gets ionized due to the applied potential difference.

ii. Ionised atoms move at high speed and hit unionized atoms among them and excite them to higher energy states.

iii. Excited atoms come back to their original states for attaining stability and emit light in the process.

Given:

Power = 800W

Voltage = 200V

For the rating given above, we will find resistance of the electric appliance.

Formula used: Power,

⇒

Now, it will offer a resistance of 50 Ω

If it works on 100V, then power consumed, will be given as:

Power =

∴ it will consume 200 W of power, if it gets 100V.

Power =

Since this is beyond the rating of the device, chances are it will burn out, but first we need to check the power generated as well.

Power =

which is beyond the rating. So, the appliance will be destroyed.

Given:

Voltage = 200V

Resistance = 200Ω

Heat generated = ?

Now, formula used:

Heat generated = Power × time

Power,

⇒ Power =

Heat generated in 5 minutes i.e. 5× 60 s i.e. 300 s

⇒ Heat = Power× time

= 200× 300 = 60000 J

= 60 kJ

Power =

Heat generated in 5 minutes i.e.5× 60 s i.e. 300 s

= Power× time

= 400× 300

= 120000 J

= 120 kJ

Power =

Heat generated in 5 minutes i.e.5× 60 s i.e. 300 s

= Power× time

= 100× 300

= 30000 J

= 30 kJ

The diagram of microwave is given below:

i. Microwave is used to cook the food. In it, microwaves, are passed through the molecules of the food.

ii. These microwaves are produced by a device called a magnetron within the microwave oven.

iii. All food items contain water. The frequency of microwaves, causes the water molecules to vibrate, as a result, this movement generates heat.

iv. When the temperature rises, the molecules of water travel or vibrate or rotate with higher energies. The frequency of rotation of water molecules is about 3 gigahertz (300 crore hertz).

v. If water receives microwaves of this frequency, its molecules absorb this radiation and water gets heated up. In this way the food gets heated up in a microwave oven.

i. Arc lamps are used in rescue operations as searchlights in areas where electrification has been disrupted.

ii. They are kind of super shot lights which can light a large area. Hence, preferred in rescue operations.

iii. Also, these are much cheaper as compared to any other light source.