Which one of the following statements is correct about Spring tides?
- (a)High tide is higher than average high tide and Low tide is higher than average low tide.
- (b)High tide is lower than average high tide and Low tide is higher than average low tide.
- (c)High tide is higher than average high tide and Low tide is lower than average low tide.
- (d)High tide is lower than average high tide and Low tide is lower than average low tide.
Correct — C, high tide higher than average and low tide lower than average. A spring tide occurs when the Sun, the Earth and the Moon lie roughly in a straight line, which happens twice a lunar month — at new moon, when the Sun and Moon are on the same side, and at full moon, when they are on opposite sides. In both positions the tide-raising pull of the Sun reinforces that of the Moon instead of working across it, so the water is heaped higher where the bulge is and drawn correspondingly lower where it is not. The result is the largest tidal range of the month: high water above the average high and low water below the average low. Neap tides are the mirror case, at first and third quarter, when the two pulls act at right angles and the range shrinks at both ends.
- (a)High tide is higher than average high tide and Low tide is higher than average low tide. — Raises the high tide but also raises the low tide, which would mean the whole water level had risen rather than the range having widened. Tides are about range, not about a change in mean level.
- (b)High tide is lower than average high tide and Low tide is higher than average low tide. — Describes a neap tide exactly — high water lower than average and low water higher than average, giving the smallest range of the month.
- (d)High tide is lower than average high tide and Low tide is lower than average low tide. — Lowers both, which again shifts the mean level rather than widening or narrowing the range, and corresponds to no tidal condition.
Tides are raised by the difference between the gravitational pull on the near side of the Earth and on the far side, and both the Moon and the Sun raise them. The Moon dominates because it is far closer, but the Sun contributes roughly half as much again, and whether that contribution adds to the lunar tide or subtracts from it depends on the geometry. Aligned bodies, whether in conjunction or in opposition, add; bodies at right angles subtract. That is the whole mechanism.
The word spring is the commonest source of confusion here and has nothing to do with the season. It comes from the old sense of springing or welling up, and spring tides occur in every month of the year, twice a month. Two refinements are worth carrying. When a spring tide coincides with the Moon at perigee, its closest approach, the range is greater still and the result is sometimes called a perigean spring tide. And a spring tide does not arrive on the instant of new or full moon everywhere, because the water takes time to respond and coastline shape modifies the timing and the height, which is why a place such as the Bay of Fundy or the Gulf of Khambhat has an extreme range while an enclosed sea has almost none.
- Spring tides occur at new moon and at full moon, when the Sun, Earth and Moon are aligned in syzygy, and produce the maximum tidal range.
- Neap tides occur at the first and third quarters, when the Sun and Moon are in quadrature, and produce the minimum tidal range.
- Spring and neap tides each occur twice in a lunar month, roughly seven days apart.
- The Moon's tide-raising force is about twice that of the Sun, because tidal force falls off with the cube of distance.
- A spring tide coinciding with lunar perigee gives an unusually large range, sometimes called a perigean spring tide.
Both kinds occur twice a lunar month; what changes is the range, not the mean sea level.
- Reading 'spring' as the season; spring tides occur throughout the year.
- Confusing a change in range with a change in mean sea level — two of the options here describe the latter and correspond to nothing.
- Assuming spring tides happen only at full moon; new moon produces them equally.
As a four-way permutation of higher and lower applied to high water and low water, so the candidate must be clear that the answer is about range at both ends and not about the level of the sea.
Assertion (A): During the Neap Tides, the high tide is lower and the low tide is higher than usual. Reason (R): The Neap Tide, unlike the Spring Tide, occurs on the New Moon instead of on the Full Moon.
- (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 a correct explanation of A
- (c) A is true, but R is false
- (d) A is false, but R is true
Answer(c) A is true, but R is false
The neap half of the same mechanism, and it carries the exact error a candidate is likeliest to make. New moon gives a spring tide, not a neap tide; the neap positions are the two quarters.
Which of the following positions of Sun, Earth and Moon is/are suitable for Spring Tide? 1. SYZYGY Conjunction 2. SYZYGY Opposition 3. Quadrature Select the correct answer using the code given below :
- (a) 1 only
- (b) 2 only
- (c) 1 and 2
- (d) 1 and 3
Answer(c) 1 and 2
The same phenomenon asked in the technical vocabulary. Conjunction is new moon and opposition is full moon, and both are alignments that give a spring tide; quadrature is the right-angled position that gives a neap.
- practice — not a real PYQ
Neap tides occur when the Sun, Earth and Moon are
- (a)in a straight line at new moon
- (b)in a straight line at full moon
- (c)at right angles, at the first and third quarters
- (d)at the Moon's perigee
Answer(c) at right angles, at the first and third quarters — the solar and lunar pulls partly cancel and the range is least.
- practice — not a real PYQ
The tide-raising force of the Moon exceeds that of the Sun mainly because
- (a)the Moon is more massive than the Sun
- (b)the Moon is far closer, and tidal force falls off with the cube of distance
- (c)the Moon rotates faster
- (d)the Moon reflects sunlight
Answer(b) the Moon is far closer, and tidal force falls off with the cube of distance.