What caused wind to deflect towards left in Southern Hemisphere?
- (a)Temperature
- (b)Pressure
- (c)Magnetic Field
- (d)Coriolis force
Correct — D, Coriolis force. Because the Earth rotates on its axis, any freely moving object — including wind — appears to be deflected from a straight path. This apparent deflection is the Coriolis force (Ferrel's Law): winds are deflected to the RIGHT in the Northern Hemisphere and to the LEFT in the Southern Hemisphere. It is zero at the equator and maximum at the poles, and it acts at right angles to wind direction. Hence the leftward deflection of Southern-Hemisphere winds is caused by the Coriolis force.
- (a)Temperature — Temperature differences create the pressure differences that set winds in motion, but they do not cause the sideways (left/right) deflection — that comes from Earth's rotation via the Coriolis effect.
- (b)Pressure — The pressure-gradient force pushes air from high to low pressure (the wind's initial direction); the deflection to the left/right is the Coriolis force, not pressure itself.
- (c)Magnetic Field — Earth's magnetic field deflects charged particles, not neutral air masses; it plays no role in deflecting winds.
The Coriolis force is an apparent (inertial) force arising from Earth's rotation. It deflects moving air to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Its magnitude equals 2 x omega x v x sin(latitude) — so it grows with wind speed and latitude, being zero at the equator (sin 0 = 0) and maximum at the poles. Together with the pressure-gradient force it produces the geostrophic wind and the rotation of cyclones.
The wind is set in motion by the pressure gradient (from temperature-driven pressure differences), but this question asks what makes it turn sideways. That deflection — to the left in the Southern Hemisphere — is uniquely the Coriolis force. The distractors name the forces that start or shape the wind, not the one that deflects it by hemisphere.
- The Coriolis force arises from Earth's rotation (Ferrel's Law).
- It deflects winds to the RIGHT in the Northern Hemisphere and to the LEFT in the Southern Hemisphere.
- It is zero at the equator, maximum at the poles, and increases with wind speed.
- It changes only the direction of wind, not its speed, and acts perpendicular to motion.
Earth's rotation deflects winds right in the Northern Hemisphere and left in the Southern Hemisphere — zero at the equator, maximum at the poles.
- Reversing the direction — Coriolis deflects RIGHT in the north and LEFT in the south.
- Attributing the deflection to pressure or temperature — those move the wind; Coriolis turns it.
UPSC/UPPSC ask the cause of wind deflection, the direction by hemisphere, or where the Coriolis force is maximum/zero (poles/equator).
Assertion (A): Wind patterns are clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere. Reason (R): The directions of wind patterns in the northern and the southern hemisphere are governed by the Coriolis Effect.
- (a) Both A and R are individually true and R is the correct explanation of A
- (b) Both A and R are individually true but R is not the correct explanation of A
- (c) A is true but R is false
- (d) A is false but R is true
Answer(a) Both A and R are individually true and R is the correct explanation of A
Same concept — the Coriolis effect governs hemispheric wind-circulation direction (clockwise in the north, anticlockwise in the south).
With reference to "Coriolis force", which of the following statements is/are correct? 1. It increases with increase in wind velocity. 2. It is maximum at the poles and is absent at the equator. Select the answer using the code given below:
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer(c) Both 1 and 2
Same Coriolis-force concept — it increases with wind velocity and is maximum at the poles, absent at the equator.
- practice — not a real PYQ
The Coriolis force is maximum at which location?
- (a)Equator
- (b)Tropics
- (c)Poles
- (d)45 degrees latitude
Answer(c) Poles — the Coriolis force is maximum at the poles and zero at the equator.
- practice — not a real PYQ
In the Northern Hemisphere, winds are deflected towards their:
- (a)Left
- (b)Right
- (c)Upward
- (d)No deflection
Answer(b) Right — Coriolis deflects winds to the right in the Northern Hemisphere.