Measurements and Experimentation **Exe-1A** System of Unit Numericals for ICSE Class-9 Concise Selina Publishers. There is the solutions of Numericals Questions of your latest textbook which is applicable in 2023-24 academic session**. **Visit official Website CISCE for detail information about ICSE Board Class-9.

**Measurements and Experimentation Exe-1 A System of Unit Numericals Questions Solutions**

**ICSE Physics for Class-9 Concise Selina Publishers**

Board | ICSE |

Class | 9 |

Subject | Physics |

Writer / Publication | Concise selina Publishers |

Chapter-1 | Measurements and Experimentation |

Exe – 1 A | System of Unit |

Topics | Solution of Exe-1(A) Numericals |

Academic Session | 2023-2024 |

System of Unit numericals problems / questions for practice, conversion of one unit into other unit in very simple and easy way. Therefore practice these important questions/ problems to learn conversion of unit in effective way.

**Exe-1A** System of Unit Numericals

Measurements and Experimentation in Physics for ICSE Class-9 of Concise Selina Publishers Chapter-1

**Page 11**

**Question 1. **The wavelength of light of a particular colour is 5800 Å. Express it in (a) nanometre and (b) metre.

**Answer : **Wavelength of light of particular colour = 5800 Å

**(a) 1 A = 10 ^{-1} nm**

5800 A = 5800 × 10^{-1} nm

= 580 nm

**(b) 1 A = 10 ^{-10} m**

5800 A= 5800 × 10^{-10} m

= 5.8 × 10^{-7} m

**Question 2. **The size of bacteria is 1 µ. Find the number of bacteria present in 1 m length.

**Answer : **Size of a bacteria = 1 µ , Since 1 µ = 10^{-6} m

Number of the particle = Total length/size of one bacteria

= 1 m/10^{-6} m = 10^{6}

**Question 3. **The distance of a galaxy is 5·6 × 10^{25} m. Assuming the speed of light to be 3 × 10^{8} m s “. Find the time taken by light to travel this distance .

[Hint : Time taken = distance/speed ]

**Answer : **Distance of galaxy = 5.6 × 10^{25} m and Speed of light = 3 × 10^{8} m/s

(a) Time taken by light = Distance travelled/speed of light

= (5.6 × 10^{25 }/ 3 × 10^{8}) s

= 1.87 × 10^{17} s

**Question 4. **The wave length of light is 589 nm. What its wavelength in Å ?

**Answer : **1 nm= 10 Å Therefore 589 nm = 10×589A°= 5890 Å

**Question 5. **The distance of the nearest star, Proxima Centauri, from the Earth is 4.0 x 10^{13} km. Express it in light year.

**Answer : **1 Light year = 9.46 x 10^{12} km

or 9.46 x 10^{12} km = 1 Light year

∴ 4.0 x 10^{13} km

= $)$ x 4.0 x 10^{13}

= 4.2 light years.

**Question 6. **It takes time 8 min for light to reach form the sun to the earth surface . If speed of light is taken to be 3 × 10^{8} m/s, find the distance from the sun to the earth in km.

**Answer : **1 Min= 60 sec So 8 Min= 8×60 = 480 sec

Now distance = Speed×Time

= 3×10^{8}×480

=1.44×10^{8} Km/s

**Question 7. **‘The distance of a star form the earth is 8.33 light minutes .’ What do you mean by this statements ? Express the distance in meter.

**Answer : **It means light take 8.33 Minute to reach the star while the speed of light is 3×10^{8} m/s.

Distance= Speed × Time

= 3×10^{8} × 8.33×60

=1.5×10^{11}Mitre

— : End of Me

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