Some Natural Phenomena Test - 8

During a lightning strike, the upper clouds become positively charged, while the lower clouds become charged negatively. As a result of the induction of the negative charges on the lower clouds, the nearby ground becomes positively charged. When the accumulation of negative charges on the lower clouds becomes very large, they get discharged to the ground through air. This discharge of negative charges to the ground results in lightning.

Hence, the correct answer is option D.

During lightning strikes, certain safety measures must be followed. Large amounts of current flow during lightning strikes. This current may hurt living organisms by means of conducting objects. Bathing should be avoided during lightning because there is a chance of the water getting charged and conducting electricity, thereby causing accident. Hence, statement I is correct.

Also, the use of electrical appliances and ground telecommunication, which involve conduction of charges through wires, should be avoided. Hence, statement II is also correct.

During lightning, a car acts like a hollow sphere. As a result, electrical charges from outside cannot affect anything inside a car. Therefore, sitting inside a car is actually a safety measure during lightning. Hence, statement III is incorrect.

The correct answer is C.

Lightning rods are nothing but metallic rods connected to the ground by a conducting wire. These are installed on top of buildings in order to conduct the charges that are discharged by the clouds to the ground. Hence, lightning rods are protective devices that protect high-rise buildings against lightning strikes.

The correct answer is A.

When an object is charged by rubbing it, the process is called charging by friction. Mukhtar rubs the comb against his dry hair. Hence, the comb becomes charged by the friction between the comb and the hair.

When a charged object is brought near an uncharged object, the uncharged object becomes charged with the opposite charge. Since unlike charges attract each other, these two objects attract each other. This is called charging by induction. Hence, when Mukhtar brings the charged comb near the paper pieces, they become charged and get attracted toward the comb. Therefore, during the given experiment, charging by both friction and induction occur.

The correct answer is C.

Seismograph is a scientific instrument that is used to measure the intensity of earthquakes. It measures the intensity by tracing and recording the vibrations of the surface of earth.

The correct answer is D.

According to statement I, object P attracts object Q. This implies that either the objects have opposite charges or one of the objects is charged and the other is uncharged. If R repels S its evident that both of them have like charges. There can be a possibility that object Q is uncharged.

Hence, the correct answer is option D.

The process of charging in which an object is charged by bringing it in contact with a charged object is called charging by conduction. For charging by conduction to occur, both the objects should be made up of conducting materials. Cardboard sheets are made up of wood, which is a non-conducting material. Therefore, a cardboard sheet cannot be charged by physical connection or by contact.

Hence, the correct answer is option D.

When an uncharged object is touched with a charged object, the uncharged object gets charged. This is caused by the transfer of charges from one object to another object. This process of charging is called charging by conduction or contact.

An electroscope works on this principal of charging by conduction. It consists of a metal strip. At its one end, two aluminium foils are attached and the other end is free. If a charged object is touched to the free end of the metal strip, then a transfer of charges will take place − from the charged object to the aluminium foils, through the strip. Since like charges repel, both the foils will move away from each other. In case an uncharged object is brought in contact with the strip, the foils will not get deflected. Therefore, an electroscope is used to detect whether an object is charged or not.

Hence, the correct answer is option C.

Clouds move in the air past one another. Hence, charges are accumulated on clouds. This process of charging involves charging by friction. The nearby high structures also get charged because of the influence of the charges on the lower clouds. This process of charging involves charging by induction. Hence, during lightning, charging by both friction and induction occur.

The correct answer is C.