Class 9 General Science Chapter 8 Question Answer

Complete Notes of Class 9 General Science Chapter 8 Question Answer Current Electricity Notes in 9th Class General Science Urdu Medium by Sir Usman Lateef Suib. These computerized notes are very helpful in the preparation of the Current Electricity Notes for students of the Class 9 General Science Chapter 8 Question Answer these are according to the new paper patterns of all Punjab boards.

• Important Multiple Choice Questions (MCQs) and Short Questions of Chapter No.8: Current electricity in General Science 9th class Urdu Medium.
• Concept of Electric Current
• Direct and Alternating Current
• Conventional Current
• Use of A.C. and D.C.
• Potential Difference
• Domestic Electric Supply
• Hazards of Electricity and Precautionary Measures
• Resistance
• Electrical Measuring Instruments
• Components of a Circuit
• Analogue and Digital Meters
• Electricity is very common form of energy, which we use in our homes and work places everyday. It has facilitated the availability of our needs of life. Just turn on the switch and the electricity starts its work.
• Electricity is used in four important ways. It causes fans, electric motors and machines to move. It provides light through bulbs, tubes and television. In a loud speaker it is converted into sound and in electric iron, heater and toaster it assumes the form of heat.
• Electric Current: You know that electric current is the flow of charges. The charges are the free electrons, which are available in conductors. In some conductors like liquids and gases, the current also flows due to the motion of positive and negative ions. But a source of energy is required to force the charges into motion. The source pushes the charges through the circuit.
• "The amount of charge that passes through any cross-section in one second is called current". If charge Q passes through any cross-section in time t seconds then the current I can be written mathematically as  l = Q / t. The unit of current in system International (SI) is ampere. It is denoted by A. Current can be measured by connecting an ammeter in series with the circuit.
• Conventional Current: From the very beginning after the discovery of electricity, it was assumed that the electric current is due to flow of positive charges, which move from positive terminal of the battery towards the negative terminal. This is called the conventional current. But, now, we know this fact very well that the charge carrying particles in metal conductors are the electrons having negative charge on them. Electrons move from negative terminal of the battery towards positive terminal. Thus in fact, the current is due to the flow of negative charges.
• Keep in mind that electrons do not flow through a conductor like a stream but their motion is different. A number of free electrons are always bumping among the atoms of the conductor, which is called random motion. In the absence of a battery, the number of electrons passing towards left is the same as through the right side. Thus net rate of electrons passing through any cross-section in one direction is zero.
• When one end of a conductor is connected to the positive terminal of the battery and the other end connected to the negative terminal, the electrons experience force. Due to this force electrons start drifting towards the positive terminal of the battery in addition to their random motion. As the electrons have negative charge, so they carry negative charge while moving through the circuit. However we can assume that  "The amount of positive charge flowing in one direction is equivalent to the same amount of charge flowing in opposite direction".
• Potential Difference: When an electric circuit is completed by closing the switch, the negative terminal of the battery pushes the free electrons in the circuit towards positive terminal. This causes the flow of current.