Insights Static Quiz -152, 2018 –Physical Geography and Environment

Answer – C

• Differences in water density affect vertical mobility of ocean currents. Denser water tends to sink, while relatively lighter water tends to rise.
• Water with high salinity is denser than water with low salinity and in the same way cold water is denser than warm water. Hence statement 2 is correct.
• Cold-water ocean currents occur when the cold water at the poles sinks and slowly moves towards the equator. Warm-water currents travel out from the equator along the surface, flowing towards the poles to replace the sinking cold water. This means that ocean currents has to have vertical mobility, which drives horizontal movement of ocean currents towards the poles. Hence statement 1 is correct.

Answer – A

• The strength of a current refers to the speed of the current. A current is usually strongest at the surface and decreases in strength (speed) with depth. Hence statement 1 is correct.
• Usually, the currents are strongest near the surface and may attain speeds over five knots. Most currents have speeds less than or equal to 5 knots. At depths, currents are generally slow with speeds less than 0.5 knots. Hence statement 2 is incorrect.

Answer – C

• Heating by solar energy causes the water to expand. That is why, near the equator the ocean water is about 8 cm higher in level than in the middle latitudes. This causes a very slight gradient and water tends to flow down the slope. Hence statement 1 is correct.
• The Coriolis force, which is due to rotation of the earth, intervenes and causes the water to move to the right in the northern hemisphere and to the left in the southern hemisphere. These large accumulations of water and the flow around them are called Gyres. These produce large circular currents in all the ocean basins. Hence statements 2 is correct.

Answer – D

• The primary forces that influence the ocean currents are:
  • heating by solar energy
  • wind – Wind blowing on the surface of the ocean pushes the water to move. Friction between the wind and the water surface affects the movement of the water body in its course.
  • gravity – Gravity tends to pull the water down the pile and create gradient variation
  • coriolis force.

Answer – C

• Since tides are caused by the earth-moon-sun positions which are known accurately, the tides can be predicted well in advance. This helps the navigators and fishermen plan their activities.
• Tidal flows are of great importance in navigation. Tidal heights are very important, especially harbours near rivers and within estuaries having shallow ‘bars’ at the entrance, which prevent ships and boats from entering into the harbour. Hence statement 1 is correct
• Tides are also helpful in desilting the sediments and in removing polluted water from river estuaries. Hence statement 2 is correct