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.

Earthquakes: Most tsunamis are caused by earthquakes that occur beneath the ocean. The size of the tsunami is related to the size of the earthquake. Shallow focus earthquakes in subduction zones are the most destructive.

Strong winds only leads to high tides, not tsunami 

• 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.

• 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.
Topic in NCERT: Do you know?
Line in NCERT: "Salinity is the amount of salt in grams present in 1000 grams of water."

Ocean waves are primarily formed by the winds blowing across the surface of the water. Here’s how it works:

• The wind transfers its energy to the water, creating ripples.
• As these ripples grow, they develop into larger waves.
• Factors such as wind speed, duration, and the distance over which the wind blows (fetch) affect the size of the waves.

• 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.

Ocean water is saline because it contains a high concentration of dissolved salts, primarily sodium chloride​.

Ocean currents are streams of water that flow continuously on the surface of the ocean in specific directions. They can be classified as either warm or cold.