1. The curve representing Ohm's law in linear.
2. The condition in Ohm's Law is that the temperature should remain constant.
3. The Ohm's Law can be applied with certain reservations to electrolytes.
4. The presence of an electric current is made known by the effects produced.
5. An electric current can neither be seen nor touched.
6. Three important effects produced by the presence of a current heating, magnetic and electric shock.
7. Thermistor has negative coefficient of resistance.
8. International ohm is defined in terms of resistance of a column of mercury.
9. Resistors commonly used in power circuits are wire wound resistors.
10. When current flows through a heater coil it glows but the supply wiring does not glow because the resistance of heater coil is more than that of supply wires.
11. If the voltage applied across an electric press is reduced by 50 percent, the power consumed by the press will be reduced by is 25 percent.
12. In a parallel circuit the potential difference across the resistance is always constant.
13. In a series circuit the current is constant.
14. Voltage applied across a circuit acts as a force.
15. The resistance of carbon filament in carbon-filament lamps increases when its temperature is decreased.
16. The heating effect of current has an undesirable side effect in a vacuum cleaner.
17. When current flows in a conductor, the heat is produced because of inter atomic collision.
18. The temperature coefficient of a conductor is defined as the increase in resistance per ohm pwer degree centigrade.
19. The value of Joule's mechanical equivalent of heat,is equal of 4.2 Joules per calorie.
20. It was experimentally found by James Precott Joule that the heat produced in a current carrying conductor is proportional to the square of current.
21. The resistance of a conductor increases when its temperature is increased.
22. The specific resistance, depends upon the nature of the material of the conductor only.
23. Resistance of a conductor increases when its length increases.
24. The resistance of conductor is the hindrance by which the conductor opposes the flow of the current.
25. The minimum requirements to cause the flow of current are a voltage source and a conductor
Some Important Characteristics of Capacitors
1.The current through capacitor is zero, if the voltage across it is not changing with time.
2. A capacitor is sort of open circuit to direct current.
3. The capacitor never dissipates energy but only stores it.
4. A capacitor resits an abrupt change in voltage across it.
5. A finite amount of energy can be stored in a capacitor even if the current through capacitor is zero, such as when the voltage across it is constant.
6. It is impossible to change the voltage across a capacitor by a finite amount in zero time, for this requires infinite current through the capacitor.
Electrostatics Question and Answer
1. Relative permitivity of vacuum is unity.
2. In the electric field, the potential is the work done in joules to bring positive charge of one coulomb from infinity to that point.
3. The unit of field intensity is newtons/coulomb.
4. Coulomb's law for the force between electric charges most closely resemble with Newton's law of gravitation.
5. Mica medium has highest value of dielectric strength.
6. The maximum value of potential gradient in cable occurs in conductor.
7.A region around a stationary electric charge has electric field.
8. Inside a hollow spherical conductor electric field is zero.
9. The effect of the dielectric is to reduce the working voltage.
10. Electrolytic capacitor is the most commonly used type but it has two disadvantages, namely low insulation resistance and suitable for Direct current only has high capacitance and low insulation resistance.
11. In a radio a gang condenser is a type of air capacitor.
12. A sphere of one metre redius can attain a maximum potential of three kilo volt.
13.The power dissipated in a pure capacitor is zero.
14. In a capacitor the eletric charge is stored in dielectric.
15. One farad is one coulomb per volt.
16. If a dielectri is placed in an electric field, the field strength decreases.
17. If the medium of a parallel plate capacitor consists of mica and air, the capacitance is increased by increasing the area of plates.
18. A capacitor with capacitance is charged through a resistance. The time constant of the charging
circuit is given by RC.
Properties of Electric Lines of Forces
A line of force is supposed to start or emanate, from a unit with a positive charge. A line of force does not form closed loop unlike a magnetic line of force. The line of force is always normal to the surface of the body at the point from where they originate or terminate. No two lines of force can across each other. An electric line of force in the same direction repel each other and those in opposite direction attract each other. There will be neutral point in this case between the two sphere. An electric line of force has a tendecy to take an easy path.
