Questions Answers Class 7 Chapter 3 Geography Maharashtra Board

Questions Answers For All Chapters – Geography Class 7

Tides

Q. 1. Prepare a chain by matching the following.

Answer:

• Waves → 8th phase of the moon (Quarter) → Objects get thrown towards the outer side.
• Centrifugal force → New moon day → Highest high tide occurs on this day.
• Gravitational force → Rotation of the earth → These are also generated due to earthquakes and volcanoes.
• Spring Tide → The moon, the sun, and the earth → The forces of the sun and the moon operate in different directions.
• Neap Tide → Wind → Operates in the direction towards the center of the earth.

Q. 2. Give geographical reasons:

(1) Tides are influenced more by the moon than the sun.

Answer:

• The gravitational force exerted by the moon on the Earth’s water bodies is stronger than that of the sun because the moon is much closer to the Earth.
• The sun’s gravitational pull is about 180 times stronger than the moon’s, but because of its great distance, its effect on tides is less.
• This is why tides are primarily influenced by the moon.

(2) At some places along the coast, the low lying areas turn into lagoons or marshy lands.

Answer:

• Continuous tidal action deposits sediments along the coast, creating low-lying areas.
• These areas may get enclosed by sandbars, restricting the flow of seawater and forming lagoons.
• In other cases, excessive deposition and vegetation growth lead to the formation of marshy lands.

(3) Place located on the opposite meridian to the place experiencing high or low tide will also experience high or low tide respectively.

Answer:

• The Earth experiences two high tides and two low tides daily due to the gravitational pull of the moon and the centrifugal force created by the Earth-moon system.
• When one side of the Earth faces the moon and experiences high tide, the opposite side also experiences a high tide due to centrifugal force.
• Similarly, when one place experiences low tide, the opposite meridian will also experience low tide.

Q. 3. Answer in brief.

(1) If there is high tide at 7 am, find the timings of the next high and low tides on the same day at a given place.

Answer:

• The tidal cycle follows a 12 hours and 25 minutes pattern.
• If high tide occurs at 7:00 AM, the next high tide will occur at approximately 7:25 PM.
• The low tides will occur in between, roughly at 1:12 PM and 1:37 AM (next day).

(2) If at Mumbai (73° E meridian), there is high tide at 1.00 pm on Thursday, then on which other meridian will there be high tide too? State with reasons.

Answer:

• High tide occurs at places on opposite meridians simultaneously.
• The opposite meridian to 73° E is 107° W (180° – 73° = 107°).
• So, at 107° W, high tide will also occur at 1:00 PM on Thursday.

(3) Explain the reasons for the generation of waves.

Answer:

• Waves are mainly generated by wind blowing across the surface of the water.
• The friction between the wind and the water surface transfers energy, creating ripples that grow into waves.
• Other factors like earthquakes, volcanic eruptions, and underwater landslides can also generate waves (e.g., tsunamis).

Q. 4. In what way will the following depend on the tides?

1. Swimming

• Tides affect the depth of coastal waters.
• During high tide, the water level rises, making it easier for swimmers to enter deeper waters.
• During low tide, shallow waters may expose rocks and marine life, which could make swimming unsafe.

2. Steering a Ship

• Ships require sufficient water depth for safe navigation.
• High tides help large ships enter and exit harbors safely.
• Low tides can make some areas too shallow for navigation, increasing the risk of ships getting stuck.

3. Fishing

• Fish move with tidal currents, making them easier to catch during high tide.
• Fishermen often prefer to cast nets during incoming and outgoing tides to maximize their catch.
• Certain fish species are more active during specific tidal phases.

4. Salt Pans

• Salt pans rely on seawater being trapped and evaporated to produce salt.
• High tides help fill salt pans with seawater.
• Low tides allow water to evaporate, leaving behind salt deposits.

5. Going to Coastal Areas for Trips

• High tides provide more opportunities for water-based activities like boating and swimming.
• Low tides expose beaches, sandbars, and tidal pools, allowing visitors to explore marine life and collect seashells.
• Tourists should be aware of tidal timings to avoid getting stranded in certain coastal areas.

Q. 5. Observe fig. 3.8 of neap tide and answer the following questions.

(1) Which phase of the moon does it show ?

Answer: The neap tide occurs during the first quarter and third quarter phases of the moon.

(2) What are the relative positions of the moon, the sun and the earth ?

Answer:

• The moon, Earth, and sun form a right angle (90°) during a neap tide.
• This weakens the gravitational pull on the water bodies.

(3) What effect will it have on the tides ?

Answer:Neap tides result in the lowest high tides and highest low tides because the sun’s and moon’s gravitational forces work against each other, reducing the tidal range.

Q. 6. Differentiate between.

(1) High tide and low tide.

Answer:

(2) Spring tide and neap tide.

Answer:

Q. 7. Describe the positive and negative effects of tides.

Answer:

Positive Effects:

• Navigation: Helps ships enter and exit harbors safely.
• Fishing: Fish are more active during high tides, making it easier for fishermen to catch them.
• Tidal Energy: Tides can be used to generate electricity.
• Coastal Cleaning: High tides help remove waste and keep coasts clean.

Negative Effects:

• Coastal Erosion: Strong tides can erode coastlines.
• Flooding: High tides combined with storms can lead to flooding.
• Navigation Hazards: Strong tides may make navigation difficult.
• Disruptions in Marine Life: Sudden tidal changes can affect marine ecosystems.