GeographyISC Class 11 · Ocean Water Movements

Tides: Origin, Timing, Spring and Neap (ISC Class 11 Geography)

Updated 17 October 2026 · Fact-checked

Tides are the regular rise and fall of the sea, mainly from the moon's pull. The side facing the moon has a direct tide and the opposite side an indirect tide, so most coasts have two highs and two lows a day, about 12 h 25 min apart. Spring tides occur at new and full moon, neap tides at the quarters.

When Sun, Moon and Earth are in line the forces add (spring, large range); at right angles they partly cancel (neap, small range).

Illustration drawn for QuestionBuddy.

Understand Tides: Origin, Timing, Spring and Neap

Origin. The moon's pull is stronger than the sun's because it is closer (about twice the tide-raising force). The earth and moon revolve about a common centre of mass, creating a centrifugal effect away from the moon. On the side facing the moon, water bulges towards it (direct or primary tide); on the opposite side, the moon's pull is weakest and the centrifugal effect dominates, giving the indirect (secondary) tide. Between the bulges are low tides.

Timing. As the earth rotates a place passes through both bulges, so most coasts have two high and two low tides a day. The moon advances in orbit, so a place faces it again after about 24 h 50 min (tidal or lunar day). Successive high tides are about 12 h 25 min apart, high and low tides about 6 h 12 min apart, and tides arrive about 50 min later each day. Some coasts have one high and one low (diurnal) or two unequal (mixed tides). Tidal range is the difference in height between high and low tide; very large in funnel-shaped bays and estuaries such as the Bay of Fundy, and in India the Gulf of Khambhat and Gulf of Kachchh.

Spring tides. At new moon and full moon, when sun, moon and earth are in line (syzygy); forces add; highest highs and lowest lows; greatest range.

Neap tides. At first and last quarter, about seven days after springs, sun and moon at right angles (quadrature); forces partly cancel; lowest range.

Other variations. Higher at perigee, lower at apogee.

Importance. Tidal currents scour harbours and river mouths and help ships reach ports like Kolkata on the Hooghly, remove sewage and silt, support fishing and salt-making, and can generate tidal energy.

Tides: Origin, Timing, Spring and Neap: key facts

Tidal timing: High to high about 12 h 25 min
High to low about 6 h 12 min
Tidal day about 24 h 50 min
Daily delay: About 50 min later each day | After n days: 50 x n min
Spring and neap: Spring: new and full moon, in line
Neap: quarters, right angles
About 7 days apart
Direct and indirect: Direct: facing the moon | Indirect: opposite side

How to answer Tides: Origin, Timing, Spring and Neap questions

Questions are 3 to 4 marks: explain two tides a day or compare spring and neap; sums use 12 h 25 min and 50 min.

1Name the force (moon's pull and centrifugal effect).
2Describe the two bulges.
3Add timing with the 12 h 25 min interval.
4Compare spring and neap with alignment and range.

Tides: Origin, Timing, Spring and Neap in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Tide timetable

Suppose a high tide occurs at 04:30 on Monday.

When is the next high tide and when is the high tide the next day?

Try it first, then show the solutionSolution

Next high = 04:30 + 12 h 25 min = 16:55.
Next day = 04:30 + 24 h 50 min = 05:20.

Answer: 16:55 the same day; 05:20 the next day.

Memory hook: Add 12 h 25 min.

Fishing plan

Suppose a boat must cross a bar only near high water.

Why must the crossing time change daily?

Try it first, then show the solutionSolution

Tides arrive about 50 minutes later each day.
So the safe time slips later each day.

Answer: High tide shifts about 50 min later daily.

Memory hook: 50 minutes later each day.

Tricks to remember Tides: Origin, Timing, Spring and Neap

Short memory aids. Say each one aloud once, then use it on a question the same day.

Two bulges, two tides
One bulge toward the moon, one away: two highs a day.
Use it when: Two tides.
Spring in a line, neap at a right angle
Spring: sun-moon-earth in a line; neap: right angle.
Use it when: Spring and neap.

Tides: Origin, Timing, Spring and Neap: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Spring tide · 1 mark · MCQBoard level

Spring tides occur when:
(a) the sun and moon are at right angles
(b) the moon is at the first quarter
(c) the sun, moon and earth are in a straight line
(d) the moon is farthest from earth

Try it first, then show the solutionSolution

New and full moon.

Answer: (c) The sun, moon and earth are in a straight line.

Example 2: Tide intervals · 2 marks · Short answerBoard level

State the interval between two successive high tides and between a high and the next low tide.

Try it first, then show the solutionSolution

About 12 hours 25 minutes between high tides.
About 6 hours 12 minutes between a high and low tide.

Answer: About 12 h 25 min and about 6 h 12 min.

Example 3: Tide times · 4 marks · Long answerHarder board level

A high tide occurs at 04:30. Find (a) the next high tide that day, (b) the first low tide after it using 6 h 12 min, and (c) the high tide at the same place 6 days later using 50 min per day.

Try it first, then show the solutionSolution

(a) 04:30 + 12 h 25 min = 16:55.
(b) 04:30 + 6 h 12 min = 10:42.
(c) 6 x 50 min = 300 min = 5 h; 04:30 + 5 h = 09:30.
The pattern shifts later each day.

Answer: (a) 16:55 (b) 10:42 (c) about 09:30.

Example 4: Spring versus neap · 4 marks · Long answerHarder board level

Distinguish between spring tides and neap tides on timing, alignment, and range.

Try it first, then show the solutionSolution

Spring: new and full moon; neap: first and last quarters.
Spring: sun, moon and earth in line; neap: right angles.
Spring: forces add; neap: forces partly cancel.
Spring: greatest range; neap: least range.

Answer: Spring: in line, greatest range; neap: right angle, least range.

Example 5: Harbour case · 5 marks · Case-basedHOTS / competency

Case: A port on a funnel-shaped estuary has a very large tidal range and ships enter on high tide. (a) Name the effect of shape. (b) Name the Indian gulf with a large range. (c) Explain one benefit and one limit of tides for this port.

Try it first, then show the solutionSolution

(a) Funnel-shaped bays and estuaries amplify the range.
(b) Gulf of Khambhat or Gulf of Kachchh.
(c) Tidal currents scour the channel and help ships, but ships must time entry to high water.

Answer: (a) Funnel shape (b) Khambhat (c) scouring helps; ships need high water.

Where students lose marks in Tides: Origin, Timing, Spring and Neap

The slips examiners see most often, and what to write instead.

Mistake: Saying the sun is the main cause
Closeness is ignored.
Do this: The moon is closer, so its tide-raising force is about twice that of the sun.
Usually costs: 1 mark.
Mistake: Spring tide means season
Name misread.
Do this: Spring tides have nothing to do with season.
Usually costs: 1 mark.
Mistake: Using 12 h for tide interval
Moon motion is ignored.
Wrong working
12 h
Right working
12 h 25 min
Do this: High tides are about 12 h 25 min apart.
Usually costs: 2 marks.

Exam tips

Give the tidal day as 24 h 50 min.
State alignment for spring and neap.
Add the tidal range example Bay of Fundy.
Show time sums clearly.

Practice questions on Tides: Origin, Timing, Spring and Neap

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Tides arrive each day about:
(a) 5 minutes later
(b) 50 minutes later
(c) 5 hours later
(d) 50 minutes earlier
Hint
Lunar day.
Answer
(b) 50 minutes later.
Q2 · 3 marks · Short answerHarder board level
A high tide is at 08:15. Find the next high tide the same day and the next day's first high tide.
Hint
Add 12 h 25 min and 24 h 50 min.
Answer
Next high = 08:15 + 12 h 25 min = 20:40. The same high tide recurs after 24 h 50 min, at 09:05 the next day.
Q3 · 4 marks · Long answerHarder board level
Explain why there is a tidal bulge on the side of the earth away from the moon.
Hint
Weakest pull, centrifugal effect.
Answer
On the far side the moon's pull is weakest; the centrifugal effect from the earth-moon revolution about their common centre dominates, so water bulges away from the moon, forming the indirect tide.
Q4 · 4 marks · Long answerHarder board level
Explain the importance of tides to ports and fishing.
Hint
Scouring, depth, silt.
Answer
Tidal currents scour harbours and river mouths and help ships reach ports like Kolkata on the Hooghly, carry away sewage and silt, and support fishing and salt-making.
Q5 · 4 marks · Case-basedHOTS / competency
Case: A shop owner sees the tide range greater than usual at full moon and smaller at the quarters. (a) Name each type. (b) Explain the change. (c) Add a lunar distance factor.
Hint
Alignment.
Answer
(a) Spring and neap tides. (b) At full moon the sun and moon pulls add; at quarters they partly cancel. (c) Tides are higher at perigee.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Tidal day?Show answer
About 24 hours 50 minutes.
2.Neap alignment?Show answer
Quarters, right angles.
3.Direct tide?Show answer
The bulge facing the moon.
4.Spring tide timing?Show answer
New and full moon.
5.Port helped by tides in West Bengal?Show answer
Kolkata on the Hooghly.

Tides: Origin, Timing, Spring and Neap: frequently asked questions

Why is the moon stronger than the sun?

It is much closer.

Does every coast have two tides?

No, some have one high and one low or mixed tides.

What is syzygy?

The straight-line alignment of sun, moon and earth.