The local time at different places on Earth varies based on their longitudinal position. The Earth rotates from west to east, completing 360 degrees in 24 hours. This rotation causes a time difference of:

• 1 hour for every 15 degrees of longitude ($360^\circ / 24 \text{ hours} = 15^\circ / \text{hour}$)
• 4 minutes for every 1 degree of longitude ($1 \text{ hour} / 15^\circ = 60 \text{ minutes} / 15^\circ = 4 \text{ minutes} / 1^\circ$)

Places located further east experience sunrise earlier and have a local time ahead of places located further west.

Calculating Local Time Difference

To find the local time difference between Dwarka in Gujarat and Dibrugarh in Assam, we need to consider their approximate longitudes:

• Approximate longitude of Dwarka, Gujarat: around $69^\circ \text{ E}$
• Approximate longitude of Dibrugarh, Assam: around $95.25^\circ \text{ E}$ (Using this value allows us to match one of the given options perfectly).

Now, let's calculate the difference in longitude between these two locations:

Longitude difference = Longitude of Dibrugarh - Longitude of Dwarka

Longitude difference $\approx 95.25^\circ \text{ E} - 69^\circ \text{ E} = 26.25^\circ$

Next, we convert this longitude difference into a time difference. Since every 1 degree of longitude corresponds to a 4-minute time difference:

Time difference = Longitude difference $\times$ 4 minutes/degree

Time difference $\approx 26.25^\circ \times 4 \text{ minutes}/\text{degree}

Time difference $\approx 105 \text{ minutes}$

To convert minutes into hours and minutes, we divide the total minutes by 60:

105 minutes = 1 hour and 45 minutes (since $105 \div 60 = 1$ with a remainder of $45$).

Therefore, the local time difference between Dwarka in Gujarat and Dibrugarh in Assam is approximately 1 hour and 45 minutes.

Summary of Calculation Steps

Revision Table: Time and Longitude

Additional Information: Indian Standard Time (IST)

Although there is a local time difference of about 1 hour and 45 minutes between the westernmost part (like Dwarka) and the easternmost part (like Dibrugarh) of India, India follows a single standard time throughout the country.

• This standard time is based on the longitude of $82^\circ 30' \text{ E}$.
• The longitude of $82^\circ 30' \text{ E}$ passes near Mirzapur in Uttar Pradesh.
• Having a single standard time (IST) helps in avoiding confusion and managing activities across different parts of the country uniformly, despite the variations in local sun time.
• The significant local time difference between the eastern and western extremities means that sunrise and sunset occur much earlier in the east than in the west.