Chapter 15 Some Natural Phenomena

(b) Copper rod

Copper rod can be easily changed by friction because it is a highly conducting material. Non- conducting materials are the only one which can be easily charged by friction.

(b) Becomes positively charged while the cloth has a negative charge.

On rubbing two objects becomes charged, they get oppositely charged. By convention it is assumed that the charge acquired by the cloth is negative and the charge acquired by the glass rod is positive.

(a) False

This statement is false because like charges repel each other whereas opposite charges attracts each other.

(b) True

This statement is true because a charged plastic straw has negative charge and a charged glass rod acquires positive charge. As we know opposite charge attract each other, so the charged glass rod attracts the charged plastic straw.

(c) False

This statement is false because a lightening conductor conducts all the atmospheric charges to the Earth directly during a lightening, leaving the building safe.

(d) False

This statement is false because there is no such instrument which detect the upcoming earthquake.

During winters, while taking off a sweater, a crackling sound is heard. This is because the particles of sweater gets charged and these particles attracts or repel each other when they comes in contact with each other. Hence, due to this attraction or repulsion, a cracking sound is produced.

The human body is a conductor, so when we touch a charged body, the charge passes through our body to the ground and the body loses its charge. This discharging phenomena is known as electric discharge.

The destructive energy of an earthquake is measured on the Richter scale. It has readings 1 to 10. An earthquake measures 3 on this scale can be recorded by a seismograph. It does not cause much damage.

Measures to protect ourselves from lightening are as follows:

1. Take shelter in a house or building.
2. Do not take a bath under running tap water.
3. Do not stand under a tree.
4. Do not touch conducting materials like electric wires, poles etc.
5. Do not use umbrella with a metallic rod.
6. Do not run across a large open field.
7. If you cannot find a safe place, squat down in a low lying place.
8. Unplug all the electrical appliances if you are at home.
9. Do not use landline phones.

When a charged balloon is placed near an another charged balloon. They repel each other due to like charges present on them. However, a charged balloon attracts an uncharged balloon because it induces an unlike charge on the near surfaces of the uncharged balloon.

An electroscope can be used to detect whether a body is charged or not. In an electroscope, two metal foils are hanged with the help of a conductor in the glass jar with lid. When a charged body touches this conductor then its charges get transferred to the metal foil and they separates due to like charges. This shows that an electroscope detect charges.

In India, earthquakes are more likely to strike in Gujrat, Rajasthan and Kashmir.

The following precautions can be taken to protect from an earthquake when we are outside our home:

1. Find a clear spot away from the buildings, trees and overhead power lines.
2. If you are in a car, do not come our till the tremors stop.
3. Ask the driver to drive the car or bus slowly to the clear spot.

The umbrella has a metallic rod with a sharp point. It is a good conductor and allows electric current to pass through it. If there is a lightening, it would be dangerous to move under the umbrella. So, I would not carry an umbrella when going out the day on which the weather department has predicted a thunderstorm.