Which of the following factors influence the ocean currents? 1. Coriolis force 2. Gravity 3. Heating by solar energy 4. Wind Select the answer using the code given below:
- (a)1 and 4 only
- (b)2 and 3 only
- (c)1, 2 and 3 only
- (d)1, 2, 3 and 4
Correct — D, 1, 2, 3 and 4. All four factors influence ocean currents. Heating by solar energy (3) sets up temperature — and therefore density — differences that start the water moving. The prevailing winds (4) are the main driving force of surface currents, dragging the water along by friction. Gravity (2) pulls the piled-up water 'downhill' along the pressure gradient. And the Coriolis force (1), arising from the earth's rotation, deflects the moving water — to the right in the Northern Hemisphere and to the left in the Southern — producing the great circular gyres. Since every listed factor plays a part, the answer is all four.
- (a)1 and 4 only — It keeps the Coriolis force and wind but wrongly drops gravity and solar heating, both of which also drive currents.
- (b)2 and 3 only — It omits wind (the chief driver of surface currents) and the Coriolis force (which shapes their direction), so it is incomplete.
- (c)1, 2 and 3 only — It leaves out wind, yet the prevailing winds are the primary driving force behind surface ocean currents.
Ocean currents are large-scale movements of surface water driven by a set of primary forces. Solar heating warms the tropics more than the poles, creating temperature and density contrasts; the prevailing winds push the surface water and are the main driver of surface currents; gravity moves water down pressure gradients where it has piled up; and the Coriolis force, born of the Earth's rotation, bends the flow into the huge clockwise (Northern Hemisphere) and anticlockwise (Southern Hemisphere) gyres. Secondary factors such as differences in water density and the shape of the ocean floor and coastlines then modify the pattern.
Because all four listed items are genuine primary forces, the reasoning is to confirm each one rather than hunt for an exception. Recognising that wind and the Coriolis force belong alongside solar heating and gravity rules out every 'only' option.
- The primary forces influencing ocean currents are heating by solar energy, wind, gravity and the Coriolis force.
- Prevailing winds are the main driving force of surface currents.
- The Coriolis force deflects currents right in the Northern Hemisphere and left in the Southern, forming the gyres.
- Solar heating creates the temperature and density differences that help set water in motion.
All four are primary forces, so the answer is 1, 2, 3 and 4 — option (d).
- Do not forget wind — it is the chief driver of surface currents, so 'only' options that drop it are wrong.
- Coriolis force sets direction, not speed; solar heating and wind set the water in motion.
Usually asked by listing driving forces and testing whether the student knows all of solar heating, wind, gravity and the Coriolis force belong.
Consider the following factors: 1. Rotation of the Earth 2. Air pressure and wind 3. Density of ocean water 4. Revolution of the Earth. Which of the above factors influence the ocean currents?
- (a) 1 and 2 only
- (b) 1, 2 and 3
- (c) 1 and 4
- (d) 2, 3 and 4
Answer(b) 1, 2 and 3 — rotation (Coriolis), air pressure and wind, and density differences drive ocean currents; the Earth's revolution does not.
Almost the identical question — the factors that influence ocean currents. UPSC's version adds the Earth's revolution as a false factor, testing the same list of driving forces.
Where is the Coriolis Effect the largest?
- (a) At the Equator
- (b) At the Tropic of Capricorn and Tropic of Cancer
- (c) At the North Pole
- (d) At 45 degree latitude in each hemisphere
Answer(c) At the North Pole
A previous NDA GAT item on the Coriolis force, which is factor 1 here — the force that deflects ocean currents into gyres.
- practice — not a real PYQ
The main driving force of surface ocean currents is:
- (a)gravity
- (b)the prevailing winds
- (c)the Moon's gravity
- (d)the shape of the coastline
Answer(b) the prevailing winds — friction between wind and the sea surface pushes the water along.
- practice — not a real PYQ
In the Northern Hemisphere, the Coriolis force deflects ocean currents to their:
- (a)left
- (b)right
- (c)no deflection occurs
- (d)vertically downward
Answer(b) right — producing the clockwise gyres of the Northern Hemisphere oceans.