Electroscope Questions

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Very Short Answers Questions [1 Mark Questions]

Ques. What is the name of the first electroscope? 

Ans. Vesorium, a pivoted needle electroscope is the first electroscope invented in the year 1600 by a British physicist William Gilbert.

Ques. To prevent the gold leaf from drafts of air, it is kept in

1. Vacuum
2. Steel vessel
3. Open atmosphere
4. Glass vessel

Ans. The correct answer is d. Glass vessel

Explanation: The gold leaf connected to the bottom of the metal rod, is kept in a glass vessel to prevent the leaf from drafts of air.

Ques. The branch of physics that studies the charges at rest is

1. Electromotive force
2. Electrostatics
3. Electromechanics
4. Electro stationery

Ans. The correct answer is b. Electrostatics

Explanation: Electrostatics is the branch of physics that deals with the study of electric force, electric field, and electric potential due to the charge at rest.

Ques. Electroscopes are also regarded as crude voltmeters.

1. Yes
2. No

Ans. The correct answer is a. Yes

Explanation: An electroscope can be considered a crude voltmeter when the electric charge of an object is equal to its capacitance.

Ques. Can an electroscope help in calculating the force between two charges?

1. Yes
2. No

Ans. The correct answer is a. Yes

Explanation: An electroscope helps in calculating the force between two charges.

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Short Answers Questions [2 Marks Questions]

Ques. Define electric charge.

Ans. Electric charge is a property of a subatomic particle due to which it can apply force on another charged or uncharged particle. A body can have two types of charge

• Positive charge
• Negative charge

Ques. Why is gold used as a leaf in a gold leaf electroscope?

Ans. Gold leaves are used in a gold leaf electroscope because gold is that gold will not corrode and it can be made in the form of a very thin sheet. This makes it more sensitive to smaller electric charges.

Ques. How can we charge an electroscope?

Ans. An electroscope can be charged by the process of conduction. In this process, a charged conductor is touched with the uncharged metal ball of the electroscope. Due to the sharing of electrons, a static charge is accumulated on the electroscope.

Ques. What are the properties of electric charge?

Ans. The followings are the properties of electric charge

• It is additive in nature
• Electric charge is always conserved in an isolated system.
• It is quantized in nature
• Like charges repel each other and unlike charges attract each other.

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Long Answers Questions [3 Marks Questions]

Ques. What are the uses of an electroscope?

Ans. The followings are the uses of an electroscope

• It is used to detect the presence of charge on a body.
• It is used to detect the nature of the charge present in a body
• It is used for the identification and comparison of electric charges between two bodies.
• It is used to calculate the magnitude of the force between two charges.

Ques. What is the difference between a pith ball electroscope and a gold leaf electroscope?

Ans. The difference between the pith-ball electroscope and the gold-leaf electroscope is mainly due to its construction.

A pith ball electroscope consists of a small non-conducting ball suspended with a silk thread. To determine whether a body has a charge or not it is brought near to the non-conducting ball. If the ball remains in an equilibrium position then the body does not have any charge. If the body has a charge then an opposite charge is induced on the ball and hence it is attracted toward the charged body. This shows the presence of charge in the body.

While a gold leaf electroscope consists of two golden leaves suspended from a metallic rod with a metal knob on the top of the rod. Whenever a charged object is touched with the metal knob the charges get transferred from the rod to the leaves which repel from each other detecting charges.

Ques. The gold leaf electroscope is charged so that it leaves somewhat diverge. What will happen if X – rays are incident on the electroscope?

Ans. X-rays are ionizing radiations, when it is exposed to the electroscope they will ionize the air molecules present in the glass flask of the electroscope.

• Initially, the gold leaves of the electroscope were charged and they somewhat diverge.
• When X-rays incident on the electroscope, the surrounding air of leaves gets ionized. 
• The charge present on the leaves moves toward the ions.
• Therefore the amount of charge present on the leaves starts to decrease.
• Hence, the divergence of the leaves decreases.

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Very Long Answers Questions [5 Marks Questions]

Ques. Which kind of electroscope is the most common and what is its application? 

Ans. The most commonly used electroscope is the Gold leaf electroscope. It is used in measuring and detecting static electricity and voltage. The various applications of Gold leaf electroscope are

• Detect charge: It is used in the detection of charge. In this process, the test material is touched on the metal cap. If the test material is charged then the gold leaves diverge and if there is no impact found in the leaves then it represents the material is uncharged.
• To determine the nature of the charge: In this process, the electroscope is first charged by either a negatively or positively charged body. Now the charged object of which the nature of the charge is to be determined is touched with the metal cap. If the leaves of the electroscope diverge, then the charged body has a similar charge to that of the electroscope. And if the leaves attract each other, the charged body has an opposite charge to that of the electroscope.
• Identify a body as a conductor or insulator: In this process, two electroscopes were needed. One of the electroscopes is charged so that its leaves repel each other. Now the test object is connected between the electroscopes. If the leaves of the second electroscope also repel each other, then the test object is a conductor, if there is no effect observed on the leaves of the second electroscope, then the test object is an insulator.

Ques. Explain the different types of electroscopes.

Ans. The different types of electroscopes are

• Pith-ball Electroscope: It consists of one or more lightweight non-conductive small balls known as pith. To determine the presence of charge on a body, it is brought near to the uncharged pith. The force of attraction between the ball and the object shows that the object is charged.
• Gold-leaf Electroscope: It consists of a metal ball on the top of a conductive rod. A parallel strip of gold leaf is attached to the other end of the rod. The whole system is kept in a glass flask to prevent them from the effect of air. This electroscope is more sensitive than a pith-ball electroscope.
• Needle Electroscope: It is made up of a plate connected to a base stand and a free-swinging needle pivoted on either side of the stand. When a charged object is placed near the plate, the needle gains the same charge and rotates away.

Ques. How does a gold leaf electroscope work?

Ans. A gold leaf electroscope consists of a vertical conducting rod that is inserted into a one-hole rubber stopper fitted at the top of a glass flask. 

• The top end of the conducting rod is connected to a metal ball and the bottom half is connected to a parallel strip of gold leaves. 
• Initially, the electroscope has no charge therefore the the leaves hang straight down. 
• Now when a charged body is touched by the metal ball of the electroscope, the charge travels through the conducting rod and spread on the gold leaves. 
• Due to the similar charges on both the leaves they repel each other which shows the body touched by the metal rod has a charge.

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