The Class 9 is an important year in a student’s life and Maharashtra State Board Social Science Geography is one of the subjects that require dedication, hard work, and practice. It’s a subject where you can score well if you are well-versed with the concepts, remember the important formulas and solving methods, and have done an ample amount of practice. Worry not! Home Revise is here to make your Class 9 journey even easier. It’s essential for students to have the right study material and notes to prepare for their board examinations, and through Home Revise, you can cover all the fundamental topics in the subject and the complete Maharashtra State Board Class 9 Social Science Geography Book syllabus.
Q1. Tick the correct box according to the salinity of the ocean water
(a) Slanting sun rays, melting snow
(b) Cloudy sky, rainfall throughout the year
(c) Clear skies for the most part, perpendicular sunrays
(d) Less supply of freshwater, desert area around
(e) Low temperatures, ample supply of river water
(f) Continental location, desert around, low rainfall
Answer a: Low.
Answer b: Low.
Answer c: High.
Answer d: High.
Answer e: Low.
Answer f: High.
Q2. Give reasons.
(a) Salinity is low in the land-locked Baltic Sea.
(b) There is higher salinity in the northern Red Sea while lower in the southern.
(c) Oceans located at the same latitude do not have the same salinity.
(d) With increasing depth, the temperature of sea water decreases to a certain limit.
(e) There are more salt-pans on the Western coast of India than its eastern coast.
(f) Salinity increases in the mid latitudinal zones.
Answer a: The water in the Baltic sea is salty because of low salinity. There is only 20% salinity in the water. The Baltic Sea is very small and shallow deep sea. At a time the Baltic ocean is covered by ice. So the area is totally freezing and winter is always going on. In the month of February, the Baltic Sea is totally covered in ice.
Answer b: The northern part of the Red Sea is more saline than the southern part because it mainly has the Gulf of Suez water which lies to the west of the Sinai Peninsula. The water from the Gulf of Suez is known to have a salinity of about 40 parts per thousand, owing in part to evaporation, and consequently a high density.
Answer c: Oceans located at the same latitude do not have the same salinity because latitudes don ’t make much differ in salinity. It ’s mostly based on the salts deposited by the rivers in its delta and the proportion and the type of organisms greatly affect the salinity.
Answer d: The sunlight doesn ’t reach the depth of the sea at the bottom so the bottom portion remains cool as compared to the top one. The water at the bottom has very negligible velocity as compared to the top ones. The kinetic energy at bottom is also found to be negligible. The sunlight can’t reach the depth of sea so the temperature of sea decreases to a certain limit with increasing depth.
Answer e: In the western coast of India there are numerous rocks and rock particles as compared to the eastern coast . These rocks and rock particles are highly concentrated in salt and salt particles . The salt pans originate from these rocks and rock particles found in the western coast and that ’s why they are in abundance in the western coast rather than eastern coast.
Answer f: Salinity is low in water bodies around the equator and polar regions. It is low because the equatorial region receives heavy rainfall that adds freshwater to the oceans. Similarly, melting of ice keeps the salinity around the polar regions low in tropical regions or mid latitudinal zones where the rate of evaporation is very high and salinity is also high.
Q3. Answer the following questions.
(a) What are the factors affecting the salinity of the sea water?
(b) Explain the distribution of salinity around the Tropic of Cancer and Tropic of Capricorn.
(c) What are the factors affecting the temperature of the sea water?
(d) Explain the changes occurring in the temperature of sea water according to the depth.
(e) Name the factors affecting salinity.
Answers a: Major factors affecting the salinity of seawater are as follows.
Answer b: There is highest salinity water along the both tropics on 23 degrees North and 23 degrees South. Evaporation is high in both tropics due to high temperature and very low precipitation. This is because all the processes that act to change salinity occur at the surface not deep in the ocean.
Answer c: The factors affecting the temperature of the sea water are:
Answer d: Sea or ocean water temperature varies according to latitudes and the depth of the ocean floor. The temperature of the ocean water near the equator is more than that of the temperature near the Arctic and the Antarctic circles. With the increasing depth the temperature of the ocean water decreases . It is because the sunlight can penetrate into the ocean only up to a depth of 200 meters. Within this depth various marine organisms are found in large numbers.
Answer e: The salinity of water in the surface layer of oceans depends mainly on evaporation and precipitation.
Q4. Explain how temperature affects the following.
(a) the density of seawater
(b) the salinity of seawater
Answer a: As temperature goes down sea water gets more dense. So, the colder the water, the more dense it is. The density of water can also be increased by salinity. Less dense water floats on top of more dense water. Near the freezing point, water expands when it heats up. So increasing temperature decreases the density of seawater.
Answer b: Temperature of seawater is affected by heat input from the sun. Salinity of seawater is affected by evaporation, precipitation, ice formation and ice melting. Evaporation increases the salinity of seawater because when seawater evaporates, the salts are left behind, thus increasing their concentration.