Q. 1. What are ocean currents?
Ans. The ocean current is the general movement of a mass of water in a defined and fixed direction over great distance.
Q. 2. How can the velocity of a wave be determined?
Ans. The velocity of a moving wave can be determined as follows :
The distance between two crests or or two successive troughs is the wave length. The time taken by a wave length to pass a fixed point is known as the wave period.
Q. 3. Distinguish between a cold and warm current.
Ans. Ocean currents are broadly of two types : Warm and cold currents. The warm currents flow from the low latitudes in tropical zones towards the high latitudes in polar areas. The cold currents flow from high latitudes to low latitudes.
Q. 4. How can the velocity of the ocean currents be measured?
Ans. Air flowing over the water surface exerts a dragging force upon the surface setting the surface, water in motion. This drag produces currents : The velocity of the ocean currents can be determined by wind velocity and dragging force.
Q. 5. If there were no ocean currents, what would have happened?
Ans. Due to absence of ocean currents, the climate, trade and marine life would not have been the same. The continent of Europe could not have pleasant climate. The temperate region would have got less rainfall. The deserts would not have been located in western margins of continents. The European ports would not have been free for trade throughout the year. Fisheries would now have been found in some areas.
Q. 6. Name the main types of wind produced waves.
Ans. According to their origin, the ocean currents are of three types :
1. Longshore Currents. When the waves break against the shore and move parallel to the shore.
2. Undertow. Seaward movement of water is known as undertow. 3. Rip Currents. Rip currents are localised streaks of returning water.
Q. 7. Describe the main characteristics of ocean currents.
Ans. Main Characteristics of Ocean Currents:
(1) According to Ferral’s law, ocean currents move to their right in the northern hemisphere and to their left in the southern hemisphere.
(2) Warm currents move towards cold seas and cold currents move towards the warm seas.
(3) In the lower latitudes, warm currents flow on the eastern shores and cold on the western shores.
(4) In the higher latitudes, warm currents move along the western shores and cold currents along eastern shores.
(5) Cold and warm currents meet along the convergence and move out along divergence.
(6) Cold currents move as sub-surface currents and warm currents move as surface currents.
Q. 8. What are icebergs? Describe the sources of icebergs.
Ans. Huge masses of floating ice are known as icebergs. These break from the ice-sheets and reach the oceans. 1/10th of the iceberg remains above seawater. There are numerous icebergs in the North Atlantic. These originate from the glaciers of Greenland. Icebergs in the southern hemisphere, originate from the Atlantic ice barrier. Alaska is also one of the sources for icebergs. These are dangerous for navigation and many accidents take place.
Q. 9. Why does Southampton (Southern Coast of England) experiences tides four times a day?
Ans. Generally tides occur twice a day. But Southampton gets tides four times a day. This area connects North Sea with Atlantic Ocean through English Channel.Tides come twice from the Atlantic Ocean and twice from the North Sea. In total, tide comes four times a day.
Q. 10. Explain the importance of tides in Hoogly river.
Ans. At the time of high tides, the water increases at the mouth of rivers. The rivers become navigable and big vessels can enter the river port. Kolkata is located along Hoogly river at a distance of 120 kms, but ships can enter the port due to tides.
Q. 11. What is a tidal bore?
Ans. The vertical wall of water in the deltas of a river is called a tidal bore. When tide enters the narrow and shallow estuary of a river, it forces the river water in the opposite direction. When the height of tidal wave increases, the flow of water rushes upstream and acts like a wall. Tidal bore is common in Hoogly river.
Q. 12. Describe the Tides of Bay of Fundy (Canada).
Ans. Tides of Bay of Fundy, Canada. The highest tides in the world occur in the Bay of Fundy in Nova Scotia, Canada. The tidal range is 15-16 metres (approximately 45-50 feet). Because there are 2 high tides and 2 low tides every day (roughly a 24 hour period) ; then a tide must come in within about a 6 hour period.
As a rough estimate, the tide rises about 8 feet (or 96 inches) an hour (48 feet divided by 6 hours). This translates to a tide which rises at more than one inch per minute. If you have walked down a beach with a steep cliff along side (which is common there), be sure to watch the tides.
Q. 13. What is the interval between two tides?
‘Tides are delayed every day by 50 minutes.’ Explain.
Ans. Tides do not occur regularly every twelve hours. They occur at an interval of 12 hours and 25 minutes.
Reasons. The moon revolves around the earth from west to east and completes one revolution in 29 days. The moon shifts away and moves a little eastward from its position in 24 hrs. Therefore, it takes an extra time (more than 24 hrs.) for the earth to bring the same point in line of the moon everyday.
So the tides are delayed by 50 minutes every day. As the tide occurs twice a day, each tide is delayed by 25 minutes. Hence high tides follow an interval of 12 hrs. 25 minutes.
Q. 14. Describe the geographical effects of tides.
Ans. Advantages :
(1) Tides keep the coasts clear of all the waste and refuse of ports.
(2) Tides keep the water in motion and so ocean water does not freeze.
(3) Tides help some of the rivers in making navigable such as St. Lawrence, Hoogly and Hudson.
(4) Tidal force may be used as a source of electricity such as in France and Japan.
(5) Tides bring many shells, animals and other things from the oceans.
(6) Tides help many big ships to reach the ports located in shallow waters. At high tides, ships can enter the harbour such as at Kolkata, London etc.
(1) Tides are sometimes harmful for ships and boats.
(2) Tides check the formation of the Deltas.
(3) Marshes are formed due to accumulation of tidal water.
(4) Tides also hinder fishing.