Grade 9 Physics – Measurement and Experimentation – Numerical Problems

Grade 9 Physics – Unit 1: Measurement and Experimentation –
Numerical Problems

Question:1
The wavelength of light of a particular color is 5800 angstrom.
Express it in:
(a) nanometer
(b) meter

Solution:
Given:
Wavelength = 5800 Å

Important Conversions:
1 Å = 10⁻¹⁰ m
1 Å = 0.1 nm
(a) Conversion to nanometer:

Formula:
1 Å = 0.1 nm
Substitution:
5800 Å = 5800 × 0.1 nm
5800 × 0.1 = 580
Answer:
Wavelength = 580 nm

(b) Conversion to meter:

Formula:
1 Å = 10⁻¹⁰ m
Substitution:
5800 Å = 5800 × 10⁻¹⁰ m
Step:
5800 = 5.8 × 10³
So,

, = 5.8 × 10³ × 10⁻¹⁰
= 5.8 × 10⁻⁷ m
Final Answers:
(a) 580 nm
(b) 5.8 × 10⁻⁷ m

Question:2

The size of a bacterium is 1 μ.
Find the number of bacteria in one metre length.

Solution:
Given:
Size of bacterium = 1 μ = 1 μm = 10⁻⁶ m
Length = 1 m
Formula:
Number of bacteria = Total length / Size of one bacterium
Substitution:
Number = 1 m / (1 × 10⁻⁶ m)
m and m cancel
Number = ⁻⁶
= 10⁶
Final Answer:
Number of bacteria = 10⁶
(or)
Number of bacteria = 10,00,000

Question:3

The distance of a galaxy from the Earth is 5.6 × 10²⁵ m.
Speed of light = 3 × 10⁸ m/s.
Find the time taken by light to travel this distance.

Solution:
Given: