Lesson Notes By Weeks and Term - Senior Secondary School 1

SUBJECT: PHYSICS

CLASS:  SS 1

DATE:

TERM: 2nd TERM

REFERENCE BOOK

• New School Physics By M.W Anyakoha
• Senior Secondary School Physics By P.N Okeke

 
WEEK SEVEN

TOPIC: Gold Leaf Electroscope and Its Uses. Lighting and Lighting Conductor

CONTENT

• Gold Leaf Electroscope

• Lighting and Lighting Conductor.

Gold Leaf Electroscope

The gold-leaf electroscope is an instrument used for testing positive and negative charges. It consists of a metal (brass) rod to which a thin gold-leaf (or aluminium leaf) is attached. The rod is surmounted by a brass disc or cap and insulated from the metal case. The leaf is protected from outside influences (like drought) by enclosing it in an earthed metal case with glass windows.

Generally, the gold-leaf can also be used to test the conducting properties of materials.

Fig. 2.1 Gold-leaf electroscope

Uses of Electroscope

1. It is used to test whether a material is a conductor or an insulator. The material is made to touch the cap. Rapid collapse means that the charges escape easily and hence the material concerned is a good conductor. A slow collapse means that it is a poor conductor. No collapse means that it is an insulator.
2. Use to test charges whether the charge is positive or negative. The gold leave electroscope to test the sign of the charge of an object. If an unknown charge is brought near to a charged electroscope and the leaf diverges more, the unknown charge is similar to the charge on the electroscope.

CHARGING AN INSULATED BODY

A neutral insulated body can be charged by two methods

1. Contact method and
2. By induction

1. Contact Method: - The method is achieved by bringing a charged object in contact with it. By so doing the neutral insulated body acquired the same type of charge as that on the charged object.
2. Induction Method: - This method is simply a process of charging a neutral body by placing a charged body near it without any contact between the two.

This process is as explained in the following steps below:

1. Bring a positive charge close to an insulated body to be charged. (Note: insulation as used here is by placing body on an insulated stand to avoid the charge induced from leaking away). Negative charges on insulated body are attracted towards the inducing charge while the positive charges are repelled away from it.
2. Earth the insulated body by momentarily touching it so that the positive charge conducts away

(ii)

(i)                               

                        (iii)

Fig. 2.2 charging by induction

1. Remove inducing charge: From observation, the negative charge will spread round leaving the body is a negatively charged body. If the inducing charge is negative, then the body will acquire a negative charge after taking the steps above.

EVALUATION

1. State two uses of an electroscope.

• Draw a well label diagram of an electroscope.

• Lighting and Lighting Conductor

The atmosphere is known to contain ions or charged particles, which have been 

produced by radiation from the sun and by what is known as cosmic radiation, which enters the atmosphere from outer space.

Lighting is a sudden discharge or neutralizing of electric charges, and it occurs when charges build up in a cloud.

The lighting conductors are long metal strips running from the spike end of a conductor on the top of a building. They are used to prevent building from destruction when struck by thunder or lightning. The conductor is a long metal rod installed or connected to the earth by means of a cable. The sharp outer point of the top gains an induced charge opposite to that in the thundercloud. The charge ionizes the nearby air and the charged air molecules flow upwards from the point. This discharges the cloud before a lightning flash occurs.

EVALUATION

1. What is the function of lighting conductors?

• Define lighting.

Reading Assignment

New School Physics pg 58 -63

WEEKEND ASSIGNMENT

1. ………………  is a device use to detect charge A. Electrophorus B. Capacitor 

1. Electroscope D. Inductor

1. A lighting conductor is used to protect a building from lighting damage. A. true 

1. false C. cannot say D. none of the above

1. …………… is the sensitive part of an electroscope A. The casing B. The cap C. The gold leaf D. The brass rod
2. The casing of an electroscope is earthed so as to screen the leaf from outside interference A. positively charge B. negatively charge C. neutral D. none of the above
3. Capacitor is a device that …………. charges A. produces B. emits C. store D. none of the above

THEORY

1. Explain the two uses of an electroscope.
2. Draw a well label diagram of an electroscope.