Topics of Interest CBSE Physics
Raj Kumar Parashari 01 Dec, 2019 Views: 442
1. What is difference between electric cell and battery?
Ans. A cell is source of potential difference, it converts chemical energy into electrical energy. A battery is a combination of cells in series.
2. Give difference between primary cell and secondary cell with example.
Ans. Cell which directly gives electrical energy from chemical energy is called a primary cell. This cannot be recharged. The common primary cells are: (a) Leclanche cell (1.5 V), (b) Daniel cell (1.12 V), (c) Dry cell (1.5 V) Cell which stores electrical energy as chemical energy and returns it back as electrical energy, is called a secondary cell. This can be recharged. (i) Lead (Acid) Accumulator, (ii) Ni-Fe (Alkali Accumulator)
3. Which primary cell can be used if a standard cell is not available and why?
Ans. A Daniel cell can be used if a standard cell is not available. Daniel cell gives small but steady current for sufficiently long time. Hence, becomes a cheap substitute for a standard cell.
4. Where is a dry cell used?
Ans. A dry cell is used in portable devices like torches and transistor radios.
5. What is short circuit of a cell? How does it harm the cell?
Ans. A cell becomes short-circuited, when its terminals are directly connected. A large current flowing from the cell may damage it.
6. What is an open circuit?
Ans. A circuit becomes an open circuit, when the key is out. No current flows in an open circuit.
7. Which material is suitable for construction of standard resistances for resistance box?
Ans. Materials used are: (i) Constantan (Cu 60%, Ni 40 %) (ii) Manganin (Cu 83%, 13%, Ni 4%)
8. What properties make a material suitable for standard resistances?
Ans. The suitable properties are:
(i) High specific resistance – lesser length of wire gives required resistance.
(ii) Low temperature coefficient of resistance – the resistance does not change appreciably with change in temperature.
9. What is a rheostat?
Ans. It is a variable resistance device and is commonly used for adjusting the strength of electric current in an electric circuit.
Questions based on Ohm’s Law
1. What are ohmic and non-ohmic resistances?
Ans. Resistances which obey Ohm’s law are called ohmic resistances e.g., metals like Cu, Al, Ag etc. at low temperature. Resistances which do not obey Ohm’s law, are called non-ohmic resistances e.g. Diodes and transistors.
2. What is effect of temperature on the resistance of a conductor, semiconductor and resistor? Also draw resistivity-temperature graph for each.
Ans. The resistance of the conductors increases, for semiconductor it decreases and for resistors it increases gradually with increase in temperature. For resistivity–temperature graph refer NCERT part-1 Page No. 104.
3. Name some substances whose resistance decreases with increase in temperature.
Ans. Resistance of semi-conductors (,) decreases with increase in temperature.
4. How do you conclude that the conductor used in experiment obeyed ohm’s law?
Ans. It is done by two results:
(i) The ratio of voltmeter reading (V) and the corresponding ammeter reading (I) comes to be constant.
(ii) A graph between V and I comes to be a straight line.
5. Why a large current is not allowed to be passed through the conductor during the experiment?
Ans. If a large current is passed (or even if a small current is passed unnecessarily for a long time), the conductor will become hot and its resistance will increases. Then the graph will not, remain a straight line.
6. Why do we use thick connecting wires?
Ans. Thick connecting wires offers negligible resistance compared to given alloy wire whose resistance to be determined.
7. What is a battery eliminator?
Ans. It is a rectifier. It converts high A.C. voltage (220 V) into low desired D. C. voltage such as 2 V, 4 V, 6 V, 8 V, 10 V, 12 V. It is a good substitute for a battery or a cell.
8. Why, alloys such as manganin or Eureka are used to make standard resistance coils?
Ans. Unknown resistance wire is made of alloy, but not of metals, because
(i) The resistivity of alloys is greater than that of metals.
(ii) The temperature coefficient of resistance of alloys is negligible than that of metals.
9. What material is chosen for rheostat wire and why?
Ans. It is constantan alloy. Because its resistivity is high and temperature coefficient of resistance is quite small.
10. What is the material of the connecting wires used in the experiment and why its uses hence resistance is low?
Ans. Copper because its resistivity is very low
11. Is there any advantage of battery eliminator over usual source of
Ans. Main advantage of battery eliminator is that steady current can be drawn at desired voltages and it does not need any charging. It is easy to handle and maintain.
12. What are the factors affecting the resistance?
Ans. The resistance depends upon length, Area of cross- section, nature of material and temperature of the conductors.
13. Can we take a metal wire in place of alloy wire whose resistance is to be measured?
Ans. No. Because large current will flow and battery will damage.