Test: Water - Class 7 MCQ

• Tides are the rise and fall of ocean water that happens twice a day. This movement is caused by the gravitational pull of the sun and the moon on the Earth's surface.
• When the water covers much of the shore by rising to its highest level, it is called high tide.
• Conversely, when the water falls to its lowest level and recedes from the shore, it is known as low tide.
• The gravitational forces of the sun and the moon are what create these tides.
• During full moon and new moon days, when the sun, the moon, and the Earth are in alignment, the tides are highest, known as spring tides.
• On the other hand, during the moon's first and last quarter, the gravitational pull of the sun and moon results in low tides, known as neap tides.

• Water changes into vapor through a process called evaporation when it gets heated up.
• As this water vapor cools down, it transforms back into liquid water through condensation.
• This continuous cycle of water changing its form and moving between the oceans, atmosphere, and land is known as the water cycle.
• It's like a natural recycling system for water on Earth, ensuring we have water to drink, for plants to grow, and for rain to fall.

a) Strong winds blowing across the ocean surface

Strong winds can cause waves on the ocean surface, but these are known as surface waves or wind-generated waves. They differ from tsunamis in that they are typically smaller in height and shorter in wavelength. Tsunamis are caused by sudden displacement of large water volumes, not just by wind action.

b) Volcanic eruptions on land (Correct Answer)

When a volcanic eruption occurs underwater or near the coast, it can displace water and generate tsunami waves. The sudden displacement of a large volume of water due to an underwater volcanic explosion or collapse can set off a tsunami. Additionally, landslides triggered by volcanic eruptions can also cause water displacement and generate tsunamis.

c) Heavy rainfall in coastal areas

Heavy rainfall does not cause tsunamis. While it can lead to flooding and increased river discharge into the ocean, it does not generate the kind of large-scale water displacement necessary to form a tsunami.

d) Freezing temperatures in the ocean

Freezing temperatures can affect sea ice formation but do not cause tsunamis. Tsunamis are generated by underwater geological activity rather than changes in water temperature or ice conditions.

Tsunamis result specifically from geological events such as underwater earthquakes, volcanic eruptions, and landslides, which rapidly displace a large volume of water.

• The water cycle is the continuous movement of water on, above, and below the surface of the Earth.
• It involves processes such as evaporation, condensation, precipitation, and runoff, maintaining a balance of water across different parts of the planet.

a) Ocean

Oceans cover about 71% of the Earth's surface and contain approximately 97% of the planet's water. However, this water is salty, with a high concentration of dissolved salts, making it unsuitable for drinking, agriculture, and most industrial uses without desalination. Therefore, oceans are not considered a source of freshwater.

b) Rivers

Rivers are significant sources of freshwater. They collect water from rainfall, melting snow, and springs, carrying it across land and into lakes, seas, or oceans. Rivers provide freshwater for drinking, irrigation, and industrial purposes and play a crucial role in the water cycle.

c) Ponds

Ponds are small bodies of still freshwater, formed naturally or artificially. They contain water that is relatively free of salt, suitable for various uses such as drinking, irrigation, and supporting aquatic life. Ponds often receive water from rain, groundwater seepage, or nearby streams.

d) Glaciers

Glaciers are massive ice formations found in polar regions and mountainous areas. They store about 69% of the world's freshwater. As glaciers slowly melt, they release freshwater into rivers and lakes, contributing to the water supply. Glacial meltwater is an important freshwater source, especially in regions dependent on seasonal melting.

In summary, while rivers, ponds, and glaciers provide freshwater, oceans do not because of their salt content.

• The Dead Sea is located in Israel. It is a landlocked salt lake bordered by Jordan to the east and Israel and the West Bank to the west.
• The high salinity of the Dead Sea prevents most aquatic life from thriving in its waters.

• The tides in the ocean are caused by the gravitational pull of the sun and the moon.
• This means that the sun and the moon's gravity pulls on the water in the ocean, causing it to rise and fall in a regular pattern.
• This is why we have high tides and low tides during different times of the day.
• So, when you see the water level at the beach changing, it's because of the sun and the moon pulling on the water.

Salinity is measured by the amount of sodium chloride found in 1,000 grams of water, if there is 1 gram of sodium chloride in 1,000 grams of water solution it is 1 part per thousand.

The total volume of water on Earth is estimated at 1.386 billion km³ (333 million cubic miles), with 97.3% being salt water and 2.5% being fresh water. Of the fresh water, only 0.3% is in liquid form on the surface.

 The freshwater resources, such as water falling from the skies and moving into streams, rivers, lakes, and groundwater, provide people with the water they need every day to live.

• In the ocean, when you see the water going up and down, that's what we call waves.
• So, when you're playing on the beach and you see the ball getting washed back to the shore by the waves, that's because the water on the surface of the ocean rises and falls alternately, just like a big blanket moving up and down gently.