The correct options are specified with question numbers.

1 = C , 2 = D , 3 = A , 4 = A , 5 = A , 6 = B , 7 = A , 8 = C , 9 = D , 10 = C , 11 = A , 12 = C , 13 = C , 14 = C , 15 = C , 16 = B , 17 = A

**Physics full notes for class 11 ch1 McQs section end.**

**Short Questions.**

**Question 1 Answer:** **Number (pie)** : The circumference of a circle by the diameter of the same circle is known as number (pie). i-e

Pie = Circumference / Diameter of circle

Generally, it is taken as 22/7

**To show that , 2 pie radian = 360 degree:**

Radian is the angle subtended at the center of a circle by an arc equal in length to it’s radius.

Now if arc length = r, then Q = 1 radian and if arc length = (2pie)r , then Q = 2pie radian here ‘2pie r’ represents the length of circular path. Thus is one circle or in one revolution we have 2pie radian i-e.

1 revolution = 2pie radian ——1

We also know that, “Degree” is the angle subtended at the center of a circle by 1/360th part of its circumference. Thus there are 360 degree in one circle (or) in one revolution.

1 revolution = 360 degree

Comparing equation 1 and equation 2, we get ,

2pie radian = 360 degree.

**Question 2 Answer: Error:**

The difference between measured value and actual value of a quantity is known as error.

**Uncertainty:**

An estimate of the possible range of an error is known as uncertainty.

**OR**

The error which arises due to natural imperfection of the experimenter, the limitation of the appratus and the changes in the environment during the measurement is known as uncertainty.

**Precision:**

The measure of the consistency of measurment is known as precision. It represents the magnitude of error in a measurment.

**Accuracy:**

“The measure of corrections of a measurement is known as acuracy”.

the accuracy means to check how the measure values is closer to the actual value. It is a relative error. It can be obtained by dividing the error with measured quantity.

The accuracy depends on the error. If the error is greater the smaller will be the accuracy of the measurements and vice versa.

The accuracy of the measurement can be increased by taking severals readings and then take their average.

**Question 3 Answer:** ” Any phenomena that repeats after regular time intervals can be used as computation.”

The several repetitve phenomena occuring naturally which could served reasonable time standards are given below:

a. The motion of earth around the sun and the its spin motion can be used as reasonable time standards.

b. Revolution of moon around the earth can be used as a time standard.

c. Characteristic vibrations of crystals such as “quartz” crystal can be used as a reasonable time standards.

d. Some other repetitive phenomena which can be adopted to define a time standards are heart beat, human pulse rate, radio-octive decay rate of some substances, changing of seasons, change of shadow of an object in the sun light etc.

Question 4. Why do we find it useful to have two units for the amount of substance i-e kilogram, mole ?

Answer: We find it useful to have two units for the amount of substance i-e kilogram and mole. It is because , in case of alrge quantity or solids or liquids , we can do measurment in kilogram easily. While in case of gases or vapours we can do measurments in mole easily.

For example, Water (liquids), Ice (solids), Vapours (gas) represents the three states of matter. In case of ice and water we can use “kilogram” as a measuring unit. While in case of gas or vapours we can use “mole” as a measuring unit.

**Question 5, 6 and 7 is missing we will add these 3 questions at the end of the last chapter.**

Question 8. Give the drawbacks to use the period of a pendulum as a time standard ?

Answer: We know that the time period of a single pendulum is given below

T = 2pie underroot l/g

Shows that the period os a single pendulum depends upon the length “l” of the string and value fo “g”.

Now in summer and winter seasons, the length “l” may be effected due to expansions or contraction respectively.

Similarly, we know that the values of “g” varies with altitude and depth. Due to variation in values of “l” and “g” the time period os simple pendulum will be effected. Due to such drawbacks we can not used the period of simple pendulum as a time standards.

Question 9. Are radians and steradian the basic units of SI ? justify your answer ?

Answer: Radians and steradians are not the absic units of SI. These are the units of purely geometrical quantities i-e plane angle and solid angle respectively. The general conference on weight and measurement has not yet classified these units either under bas units or derived units. These are called supplementary units .

**Question 10 Answer:** “Micro” means very small. Micro waves have the shortest wavelengths of all the radio waves, therefore these are known as micro waves.

Now like all electromagnetic waves, the micro waves produces heating effect where their energy is absorbed . It is because , due to shorter wave length, the micro wves posses high frequency and miximum energy.

The water will absorbs microwaves of are particular frequency. This principal is used in micro wave ovens, where micro waves penetrate deep into food and heat up the water in it.

Question 11 missing you will find it at the end of last chapter.

**Question 12 Answer:** The anologous statement in that, “the results of an experimental data which is as accurate as measurement can be used in the computation.”

**OR**

“The accuracy of the final result cannot be greater than the least accurate measurements.”

**Question 13 Answer:** **Light year:**

Light year is the unit of distance. It is defined as, ” the distance travelled by light in vaccum in one year”.

1 light year = 9.46 x 10 power 15 m

**Year:**

Year is the unit of time. It is defined as, ” the time interval in which the earth completes are revolution around the sun”

1year = 365.25 days.

**Physics full notes for class 11 ch1 short questions end.**

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