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12th Class Chapter 2 Physics Short Questions

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Question: 1
What is ohmic and non ohmic devices with example.
Answer: 1
1-35
The devices which obey Ohm's law are called ohmic devices and devices which do not obey Ohm's law are called non-ohmic law.For example copper,silver and gold are ohmic whereas diodes and tungsten filaments are non ohmic.
Question: 2
State Ohm's law and write its formula.
Answer: 2
2-35
It states that "the current flowing through a conductor is directly proportional to the applied potential difference provided that the physical state remains same"
V=IR
Resistance: The opposition against the flow of current is known as resistance.The SI unit of resistance is Ohm
R=V/I
Question: 3
Name any four source of current.
Answer: 3
3-35
Source of current are
  1. Cells
  2. Electric generators
  3. Thermocouples
  4. Solar cells
Question: 4
What is the conventional current? How does it differs from electric current?
Answer: 4
4-35
The current flow due to positive charges from a point at higher potential to a point at lower potential is called conventional current.It is due to positive charges while electric current is due to negative charges i.e electrons.
Question: 5
Name some effects of current.
Answer: 5
5-35
Some effects are :
  1. Heating effects
  2. Magnetic effect
  3. Chemical effect
Question: 6
What are non ohmic devices?Give two examples.
Answer: 6
6-35
Those devices which don't obey the Ohm's law are called non-ohmic devices.Their current-voltage graphic is not a straight line.For example ,filament bulb and semiconductor diodes.
Question: 7
What are the difficulties in testing weather the filament of lighted bulb obeys ohm's law?
Answer: 7
7-35
In case of light bulb,the temperature of the filament increase with the passage of current through it.Hence the Ohms law can't be applied to filament bulb.
Question: 8
Differentiate between conventional and non-conventional current.
Answer: 8
8-35
Conventional Current: The current flow die to positive charges from a point at higher potential to a point at lower potential is called conventional current.
Question: 9
What does the equation H=I2Rt show?
Answer: 9
9-35
This equation show the heating effect,During their motion free electrons collide frequently with the atom of metal.on each collision they transfer some of their kinetic energy to the atom with which they collide.And these collisions produce heating effect in the wire.
Question: 10
Write about any two sources of Current.
Answer: 10
10-35
  1. Electric generators convert mechanical energy into the electrical energy.
  2. Solar cells convert sunlight directly into electrical energy.
  3. Thermocouples convert heat energy into electrical energy.
Question: 11
Do two long and parallel current carrying wires attract each other?
Answer: 11
11-35
Yes ,If the direction of current is same in two long parallel current carrying wires.Because the opposite pole of electromagnet comes in front of each other and attracts.
Question: 12
What is short circuit and open circuit mean to you?
Answer: 12
12-35
when switched is close and current is passing through the circuit,It is called closed circuit and in this situation resistance is zero whereas the circuit is said to be open if it has infinite resistance and no current is passing through it.
Question: 13
How the heating effects produce when current flows through the conductor?
Answer: 13
13-35
During their motion free electrons collide frequently with the atoms of metal,on each collision they transfer some of their kinetic energy to the atime with which they collide.And these collisions produce heating effect in the wire.
Question: 14
A voltmeter can not read the exact EMF of the cell.Why?
Answer: 14
14-35
When a voltmeter is connected across a cell,it will draw some current from the cell and small potential drop takes place due current flowing through the internal resistance of the cell.As a result the actual emf of the cell decrease and the voltmeter cannot read exact value.
Question: 15
What is thermistor? Gives its two applications.
Answer: 15
15-35
Thermistors are heat sensitive resistors.Thermistors with positive temperature coefficient of resistance as well as negative temperature coefficient of resistance are available.They are used for accurate measuring of temperature up to 10K.They are used as temperature sensors.
Question: 16
Does the bends in wire effect its electrical resistance?
Answer: 16
16-35
No bend in wire do not affect its electrical resistance.
Question: 17
What is meant by tolerance of resistors?
Answer: 17
17-35
Tolerance is the measure of possible variation from the marked value,A gold band has +-5% tolerance ,silver has +-10% and no band at all wounf mean a +-20 tolerance.
Question: 18
What is the effect on drift velocity of free electrons by increasing potential difference?
Answer: 18
18-35
By an increase in potential difference,drift velocity also increase.Because by increasing potential difference ,the current also increase .
Question: 19
How can rheostat be used as potential divider?
Answer: 19
19-35
By adjusting the sliding contact resistance of the rheostat can be altered which in turn would regulate the potential offered by the cell E to the main circuit,And thus a rheostat can be used as potential divider.
Question: 20
Define temperature coefficient of resistivity.
Answer: 20
20-35
The temperature of coefficient of resistivity is defined as fractional change in resistivity per kelvin rise in temperature.Its unit is K-1.
Question: 21
Differentiate between resistance and resistivity.Give their unit.
Answer: 21
21-35
Resistance: The opposition against the flow of current is known as resistance,The SI unit of resistance is Ohm.
R=V/I

Question: 22
What is meant by Tolerance? Also give one example.
Answer: 22
22-35
Tolerance mean the possible variation in the value of resistance of a carbon resistors from a marked value.In case of silver and gold ban its value is +-10% and +-5% .
Question: 23
What is the negative coefficient of temperature?
Answer: 23
23-35
If the resistance of a substance decrease with an increase in temperature ,then it is termed as negative coefficient of temperature,For example ,silicon and germanium have negative coefficient of temperature.
Question: 24
Why does the resistance of a conductor rise with a temperature?
Answer: 24
24-35
As the temperature of the conductor rises,the amplitude of vibration of atoms increase and hence the probability of their collision with free electrons also increases which results in increase of resistance of conductor.
Question: 25
What is meant by tolerance?
Answer: 25
25-35
Tolerance means the possible variation from the marked value.
Question: 26
Why does no current pass through Galvanometer in a balanced wheat stone bridge although the keys in the circuit are closed ?
Answer: 26
26-35
No current pass through the galvanometer when wheat stone bridge is balanced.Because at this stage ,both the terminals of the galvanometer are at the same potential.Hence no current will flow through it.
Question: 27
A potential difference is applied across the ends of a copper wire,What is the effect on the drift velocity of free electrons by decreasing the length and temperature of the wire?
Answer: 27
27-35
By decreasing the length and temperature of wire the value of resistance in the wire also decrease which cause an increase in the value of current,Hence the drift velocity of free electrons also increase.
Question: 28
Give two substance having negative temperature coefficient.Also define the temperature coefficient.
Answer: 28
28-35
The temperature coefficient of a resistance is defined as fractional change in resistance per kelvin rise in temperature.Its unit is K-1.Substance like Ge and Si have negative temperature coefficient.
Question: 29
State Ohm's law and basic principle of electroplating.
Answer: 29
29-35
Current passing through a wire is directly proportional to the potential difference applied across its ends provided that the physical state conductors remains same.
Basic principle of electroplating is a process of coating a thin layer of sum expensive metal of (gold,silver etc) on a article of some cheap metal.
Question: 30
Define resistivity and electrolysis.
Answer: 30
30-35
The resistance of a meter cube of a material is called resistivity.Certain liquids such dilute sulphuric acid or copper sulphate solution conduct electricity due to some chemical reactions that take place within them.The study of this process is known as electrolysis.
Question: 31
Why potential meter is accurate measuring meter?
Answer: 31
31-35
The voltage measured using potentiometer is the voltage across the terminal of the cell when current is not following through it.This voltage is exactly the emf of the cell.Further the accuracy of a potentiometer can be increased to a great extent by increasing the length of the "potentiometer wire".
Question: 32
How a wheatstone bridge is used to determine an unknown resistance?
Answer: 32
32-35
Wheatstone bridge is an especially designed electrically circuit used to calculate the accurate value of any unknown resistance.It consists of four resistance,a galvanometer, a battery and a switch connected.When the switch is closed current pas through the galvanometer and then the three known resistance R1,R2and R3are adjusted in such a way that galvanometer show no deflection,In this balanced condition the fourth unknown resistance R4can be calculated by using this relation.R1/R2=R3/R4.
Question: 33
Briefly describe the current through a metallic conductor and drift velocity.
Answer: 33
33-35
In a metallic conductor,free electron are in random motion with the speed of several hundred km/s at the room temperature.If the ends of the wire are connected to the battery the free electrons are experience a force and directed to move in the electric field direction.The accelerating electrons keep on colliding with atoms of the conductors and transfer their energy to the lattice with the result that the electrons acquire an average velocity called drift velocity.The drift velocity is of the order of 10-3.A steady current is establish in the wire.
Question: 34
What is wheat stone bridge?
Answer: 34
34-35
It is an electrical circuit which can be used to find the unknown resistance of a wire.It consists of four resistance connected in the form of mesh.galvanometer,battery and switch.
Question: 35
Define Electromotive force and Terminal potential difference.
Answer: 35
35-35
Electromotive force:The energy supplied to a unit charge in moving it from negative to positive electrode inside the source is called electromotive force.

12th Class Physics Chapters Short Questions