ICSE-IX-Physics
09: Current Electricity
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- #Section : A
- Qstn #2Distinguish between D.C. and A.C.Ans : Direct current (D.C.) is a current of constant magnitude flowing in one direction but alternating current (A.C.) is a current which reverses its magnitude and direction with time.
- Qstn #3What is an electric cell?Ans : An electric cell is a device which converts chemical energy into electrical energy. When connected in a circuit, it acts as a source of D.C. current.
- Qstn #4What transformation of energy takes place when current is drawn from a cell?Ans : Chemical energy changes into electrical energy.
- Qstn #5Name the constituents of a cell.Ans : Constituents of cell: Two electrodes and an electrolyte in a vessel.
- Qstn #6State the two kinds of cell. Give one example of each.Ans : Two kinds of cells:
(a) Primary cell: e.g. Leclanche cell
(b) Secondary cell: Lead (or acid) accumulator
- Qstn #7What is a primary cell? Name two such cells.Ans : Primary cells are cells which provide current as a result of irreversible chemical current.
Examples: Simple Voltaic cell and Leclanche cell.
- Qstn #8What is a secondary cell? Name one such cell.Ans : Secondary cells are cells which provide current as a result of reversible chemical reactions. It converts electrical energy into chemical energy when current is passed in it (i.e. during charging), while it converts chemical energy into electrical energy when current is drawn from it (i.e., during discharging).
Example: Lead (or acid) accumulator.
- Qstn #9State three differences between the primary and secondary cells.Ans :
Primary Cell Secondary cell 1. Chemical reaction is irreversible. 2. Only chemical energy is converted into electrical energy when current is drawn from it. 3. It cannot be recharged and its internal resistance is high. 1. Chemical reaction is reversible. 2. It converts electrical energy into chemical energy when current is passed in it (i.e., during charging), while converts chemical energy into electrical energy when current is drawn from it (i.e., during discharging). 3. It can be recharged and its internal resistance is low.
- Qstn #10What do you understand by the term current? State and define its S.I. unit.Ans :
- Current is the rate of flow of charge across a cross-section. It is a scalar quantity.
- Its S.I. unit is ampere (coulomb per second).
- If 1 ampere current flows through a conductor, it means that 6.25×1018 electrons pass in 1 second across that cross-section of conductor.
- Qstn #12n electrons flow through a cross section of a conductor in time t. If charge on an electron is e, then write an expression for the current in the conductor.Ans : Current, I = n e/t
- Qstn #13Name the instrument used to control the current in an electric circuit.Ans : A rheostat is used to control current in an electric circuit.
- Qstn #14In the electric circuit shown in Fig., label the parts A, B, C, D, E, and F. State the function of each part. Show in the diagram the direction of flow of current.
Ans : A: Ammeter - It measures the current flowing through the circuit.
B: Cell - It acts as a source of direct current for the circuit.
C: Key - It is used to put the current on and off in the circuit.
D: Load - It is an appliance connected in a circuit. It may just be a resistance (e.g., bulb) or a combination of different electrical components.
E: Voltmeter - It is used to measure the potential difference between two points of a circuit.
F: Rheostat - It is used to control the current in the circuit.
