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Candela (cd) is SI unit of Luminous Intensity 

The magnitude of an electric current is the amount of electric charges flowing through a conductor in one second.

Correct answer is (b) Precision

Mole is defined as the amount of substance, which contains 6.023 x 10²³ entities.

(a) International system of units

1. Amount of substance is a measure of the number of entities (particles) present in a substance.

2. The SI unit of amount of substance is mole and it is denoted as 'mol'.

Difference between Plane Angle and Solid Angle: 

Plane Angle:

• Angle between the intersection of two lines or planes. 
• It is two dimensional 
• Unit is radian.

Solid Angle: 

• Angle between the intersection of three or more planes at a common point. 
• It is three dimensional. 
• Unit is steradian.

At very low temperature, around 30 K (-243.2° C), some conductors conduct electric current without any loss. These conductors are known as 'SUPER CONDUCTORS'.

1. The magnitude of an electric current is the amount of electric charges flowing through a conductor in one second.

Electric current = \(\frac{Amount\, of \, electric charges (Q)}{time (t)}\)

I = \(\frac{Q}{t}\)

2. SI unit of electric current is 'ampere' and it is denoted as A.

1. Measurement

2. Metric 

3. British

4. kinetic energy

5. Lower

A (ampere) is the symbol for unit of electric current ?

1. Steradian

2. Scientists 

3. Temperature 

4. Ammeter 

5. One mole 

6. Solid angle 

7. Electronic 

8. Error 

9. Accuracy 

10. plane angle

1. Physicians use 'clinical thermometers'. It is graduated in 'Fahrenheit Scale'.

2. Scientists are using thermometers with kelvin scale.

1. The SI unit of Temperature is Kelvin.

2. It's symbol is 'K'.

(b) A number and a unit

(iii) (R – r) units

Answer is (i) 2 : 1

Answer is (iv) radius

(i) π(R² – r2) sq. units

(iv) πn² sq.units

(a) Both assertion and reason are true and the reason is the correct explanation of the assertion

(b) Both assertion and reason are true, but the reason is not the correct explanation of the assertion

Correct answer is (c) kelvin

One ampere is defined as one ‘coulomb’ of charge moving in a conductor in one second.

Temperature is a measure of the average kinetic energy of the particles in a system.

Thermometer is an instrument which is used for measurement of temperature.

Some common systems of units are: 

1. FPS – System (Foot for length, Pound for mass and Second for time)

2. CGS – System (Centimetre for length, Gram for mass and Second for time) 

3. MKS – System (Metre for length, Kilogram for mass and Second for time)

60 minutes = 1 hr 

1 minute = \(\frac{1}{60}\) = 0.0167 hours.

One time ‘minute hand’ rotate in one hour?

Analog clock and digital clock.

Periodic vibrations.

Physics is the study of nature and natural phenomena.

FPS system  is the British system of units.

There are Seven  base quantity.

(b) Derived quantities

1. Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory, located at Greenwich in london.

2. It is measured at the longitude of zero degree.

3. The Earth is divided into 24 Zones, each of the width of 15 degree lingitude.

4. These regions are called as Times 'Zones' Time difference between two adjacent time zone is 1 hour.

1. Approximation is the process of finding a number, which is acceptably close to the exact value of the measurement of a physical quantity.

2. It is an estimation of a number obtained by rounding off a number to its nearest place value.

3. When the data are inadequate, physicists are in need of an approximation to find the solution for problems.

4. Approximations are usually based on certain assumptions having a scientific background and they can be modified whenever accuracy is needed.

(a) Approximation gives accurate value.

880m + 620 m = 1500 m

= 1km 500 m

∴ 20 km 500 m

1. The SI unit of temperature is the kelvin (K). Temperature is also expressed in °C (degree Celsius) and °F (degree Fahrenheit).

\(\cfrac{F-32}{9}\) = \(\cfrac{C}5\); K = C + 273.15

∴ F = \(\cfrac{9}5\) C + 32 = \(\cfrac{9}5\) (K - 273.15) + 32

Here, C denotes temperature in °C, F denotes temperature in 0F and K denotes temperature in K (kelvin).

Notes: 

(i) The unît degree Celsius is named in honour of Anders Celsius (1701 – 44) Swedish astronomer. He devised a temperature scale in 1742. 

(ii) The unit degree Fahrenheit is named in honour of Gabriel Daniel Fahrenheit (1686 – 1736) German physicist. He developed the mercury thermometer and devised the temperature scale.

(iii) The unit kelvin is named in honour of William Thomson, 1st Baron Kelvin (of Largs) (1824 – 1907) British physicist and electrical engineer. He made significant contribution in thermodynamics and electromagnetic theory. He proposed a scale of temperature now known as the Kelvin scale or thermodynamic scale.

Temperature is expressed in °C (degree Celsius), °F (degree Fahrenheit) and K (kelvin).

Specific heat is expressed in J/(kg.°C).

The freezing point of water is 32 °F.

(i) False. (The temperature of a substance is measured in °C or °F or K.)

(ii) True.

(iii) True.

Area, volume, density.

A quantity that can be measured is called a physical quantity. 

For example, the length of a piece of cloth, the time at which school begins.

1. Fundamental quantity 

2. Derived quantity.

1. denser 

2. rarer 

3. graph sheet 

4. cubic metre or m³ 

5. kg/m³

6. g/cm³ 

7. floats 

8. sinks

9. 3.155 x 10⁷ second 

10. 149.6

Mass of silver (M) = ? 

Volume of silver (V) =50 cm³ 

Density of silver D = 10.5 g/cm³

Density (D) = \(\frac{mass(m)}{volume(v)}\)

mass (M) = Density × Volume 

= 10.5 x 50 = 525 g

Density =\(\frac{mass}{volume}\)