# Class 7 Geography Lesson 3 Tides answers

Maharashtra Board Class 7 Geography Solutions Chapter 3 Tides

Balbharti Maharashtra State Board Class 7 Geography Solutions Chapter 3 Tides Questions and Answers.

Maharashtra State Board Class 7 Geography Solutions Chapter 3 Tides

Class 7 Geography Chapter 3 Tides Textbook Questions and Answers

Class 7 Geography Lesson 3 Tides answers

### Exercise:

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

 Group ‘A’ Group ‘B’ Group ‘C’ (1) Waves (a) 8th phase of the moon (Quarter) (i) Objects get thrown towards the outer side. (2) Centrifugal force (b) Newmoon day (ii) Highest high tide occurs on this day. (3) Gravitational force (c) Rotation of the earth (iii) These are also generated due to earthquakes and volcanoes. (4) Spring Tide (d) The moon, the sun and the earth (iv) The forces of the sun and the moon operate in different directions. (5) Neap tide (e) Wind (v) Operates in the direction towards the centre of the earth.

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

Q. 2. Give geographical reasons:

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

(i)  The gravitational pull of the moon and the sun as well as that of the earth is one of the factors for the occurrence of tides.

(ii) The moon is closer to the earth than the sun.

(iii) Hence its gravitational force becomes more effective than that of the sun.

(iv) Therefore, tides are influenced more by the moon than the sun.

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

(i)  Some of the areas along the sea coast that are low lying get flooded easily by the sea water during high tide.

(ii) Over a period of time the accumulation of sea water leads to the formation of swamps.

(iii) Which in turn leads to formation of lagoons or marshy lands.

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

(i) The moon is closer to the earth than the sun, hence its gravitational force becomes more effective than that of the sun.

(ii)Tides occur due to the relative positions of the moon, the sun and the earth.

(iii) Therefore, a place on the earth located at the opposite point of the place experiencing high or low tide also experiences high or low tide respectively at the same time.

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

(i) High tide and low tide occurs twice in 24 hours

(ii) One cycle of high tide and low tide is completed after every 12 hours & 25 minutes.

(iii)) If there is a high tide at 7 am, the next low tide will be at 1.12pm & next high tide will be at 7.25pm.

(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.

Ans:  The other meridian which will experience high tide will be 107°W because it is exactly 180° opposite from 73°E. This is because a place on the earth located at the opposite point of the place experiencing high or low tide also experiences high or low tide respectively at the same time.

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

Ans: The main reason of wave generation is wind, but at times, due to earthquakes or volcanic eruptions occurring below the floor of the sea, waves get generated. Such waves assume a great height in the shallow waters near the coast. These waves are very destructive. They cause huge loss of property and life. These waves are called tsunamis.

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

(1) Swimming: Lack of understanding the timing of high tide and low tide may cause accidents for the swimmers entering into sea.

(2) Steering a ship: Ships can move up to the ports during the high tide.

(3) Fishing: With the high tide, fish move into the creeks and this helps the fishing activity.

(4) Salt pans: During high tide the seawater can be stored in the saltpans from which salt can be obtained.

(5) Going to coastal areas for trips: Plan for going out for trips after the full moon or new moon day. Should have details about the timing of the tide before the enjoyment.

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 diagram shows the phase of the quarter moon.

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

Ans: The moon, the sun and the earth make an angle of 90°

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

Ans: It will lead to a neap tide. Due to such conditions during high tide the water level will rise less than usual while during low tide water level will fall less than usual.

Q. 6. Differentiate between

(1) High tide and low tide.

 High tide Low tide 1. A rise in the level of sea water at a particular place is called high tide. 1. A fall in the level of sea water at a particular place is called low tide. 2. Sea water is very close to the coast 2. Sea water is far away from the coast

(2) Spring tide and neap tide.

 Spring tide Neap Tide (i) It occurs on the new moon day and the full moon day. (i) It occurs on the the first and the third quarter days. (ii) The gravitational pull of the moon and the sun as well as that of the earth are in a straight line and act in the same direction. (i) The gravitational pull of the moon and the sun are at right angle. (iii) Spring tides are a little higher than the average high tides and a little lower than the average low tides. (iii) Neap tides are a little lower than the average high tides and little higher than the average low tides.

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

Positive effects of tides

1. The tides clear the waste and hence the coasts become clean.
2. Ports do not get filled with sediments.
3. Ships can move up to the ports during high tide.
4. During high tide, sea water can be stored in salt pans from which salt can be obtained.
5. The tidal force can be used to generate electricity.

Negative effects of tides

1. A lack of understanding of the timing of high and low tides may cause accidents to swimmers entering into sea.

### Activities:

(1) Visit the nearest sea coast. From a higher location, observe the waves approaching the coast. See if the approaching waves change their direction. With the help of your teacher, find the answer to why this change occurs.

(2) Collect information from the internet about how electricity is generated from waves. Find places where such electricity is being generated.