Class 11 Geography (Fundamental of Physical Geography) Chapter 13 Movements Of Ocean Water

Key Concept: Basic Forces

a) Heating by solar energy

[Solution Description]

The primary forces influencing ocean water movement include heating by solar energy, wind, gravity, and Coriolis force. Among the options given, solar energy causes water expansion and creates gradients which are fundamental to initiating ocean currents.

Key Concept: Wave Basics

b) 2 meters

[Solution Description] The wave amplitude is calculated as one-half of the wave height. Given that the wave height is 4 meters, the amplitude is $$\frac{4}{2} = 2$$ meters.

Key Concept: Tidal Forces

b) Moon

[Solution Description]

The gravitational pull of the moon is the primary force that creates tidal bulges on Earth. While the sun also influences tides, its effect is less pronounced compared to the moon’s.

Key Concept: Current Temperature Effects

b) They decrease precipitation and create drier conditions

[Solution Description] Cold ocean currents lower the temperature of the air above them, which often results in drier conditions on the adjacent coastlines by reducing evaporation rates. This can lead to arid climates or desertification in those areas.

Key Concept: Surface Currents

d) 10%

[Solution Description]

Surface currents are primarily those occurring in the upper part of the ocean, generally constituting about 10% of all the water in the ocean. They are mainly influenced by wind friction acting on the surface of the sea.

Key Concept: Basic Definition

a) Crest

[Solution Description] The top part of a wave is known as the crest. It is the highest point in a wave cycle.

Key Concept: Ocean Current Influences

d) Centrifugal force

[Solution Description] Ocean currents are mainly influenced by solar heating, wind, gravity, and Coriolis force. Solar heating contributes to temperature differences causing density variations, wind provides momentum, gravity pulls water downhill, and the Coriolis force alters the direction of currents. Centrifugal force is involved in tidal movements but not directly in ocean currents.

Key Concept: Tidal Height

c) Position of the sun and moon

[Solution Description] The height of rising water during high tide is primarily affected by the position of the sun and moon. When these celestial bodies are aligned, their combined gravitational force results in higher high tides known as spring tides.

Key Concept: Wave Height

d) Wave height

[Solution Description]

The term used to describe the vertical distance from the bottom of a trough to the top of a crest is “wave height”. This measurement captures the full vertical extent of the wave.

Key Concept: Wave Formation

c) Friction with the sea floor

[Solution Description]

As waves move toward the shore, they encounter shallower water. The wave slows down due to friction with the sea floor. When the depth of the water is less than half the wavelength of the wave, the bottom part of the wave slows significantly while the top continues at its original speed, causing the wave to topple over and break.

Key Concept: Spring Tides Timing

b) Full moon and new moon

[Solution Description] Spring tides occur when the sun, moon, and earth are aligned, resulting in higher than normal tides. This alignment happens during the full moon and new moon phases.

Key Concept: Basic Definitions

c) Wavelength

[Solution Description] The horizontal distance between two successive crests or troughs of a wave is known as the wavelength. It is a key characteristic that defines the spatial extent of one complete cycle of a wave.

Key Concept: Basic Definition

c) During first and last quarter moon

[Solution Description] Neap tides occur when the sun and the moon are at right angles to each other which happens during the first quarter and last quarter moon phases.

Key Concept: Tidal Prediction

d) Known positions of the earth, moon, and sun

[Solution Description] Tides can be predicted well in advance due to the known positions of the earth, moon, and sun. These celestial bodies follow regular and predictable orbits, allowing for accurate calculations of tidal patterns.

Key Concept: Basic Influence

d) Warm currents

[Solution Description] Warm ocean currents transport heat from the equator towards the poles, thus warming the coastal regions as they flow past them.

Key Concept: Wave Measurement

b) 2 meters

[Solution Description] The wave amplitude is calculated as half of the wave height. Given that the wave height is 4 meters, the wave amplitude can be calculated as follows: $\text{Wave Amplitude} = \frac{\text{Wave Height}}{2} = \frac{4}{2} = 2$ meters.

Key Concept: Temperature Classification

b) Warm current

[Solution Description] Warm currents bring warm water from equatorial regions to colder polar regions, thereby warming them.

Key Concept: Basic Definition

b) Spring tides

[Solution Description] When the sun, moon, and earth are in a straight line, the combined gravitational forces result in higher high tides and lower low tides, known as spring tides.

Key Concept: Tidal Forces

c) Sun and Moon

[Solution Description] Tides are caused by the gravitational forces exerted by the sun and the moon on Earth’s oceans. However, the moon has a more significant impact due to its proximity.

Key Concept: Ocean Currents

c) Primary forces like solar energy, wind, and Coriolis force

[Solution Description] Ocean currents are primarily influenced by solar energy, wind, gravity, and the Coriolis force, which drive the continuous flow of water in the oceans.

Key Concept: Basic Terms

c) Wave period

[Solution Description] A wave period is the time taken for a full cycle of the wave to pass a specific point. It measures the duration over which a wave crest and trough move past.

Key Concept: Wave Speed

c) 5 m/s

[Solution Description]

To find the wave speed $v$, use the formula:

$v = \frac{\text{Wavelength}}{\text{Period}}$

Given the wavelength is 20 meters and the period is 4 seconds:

$v = \frac{20 \, \text{meters}}{4 \, \text{seconds}} = 5 \, \text{m/s}$

Therefore, the wave speed is 5 m/s.

Key Concept: Basic Definition

b) 10%

[Solution Description] Surface currents make up about 10% of the ocean’s total volume, while deep water currents account for the remaining 90\%.

Key Concept: Basic Definition

c) Perigee

[Solution Description] The term for the point in the moon’s orbit where it is closest to Earth is called “perigee.” At this position, the gravitational pull of the moon on Earth’s waters is stronger, resulting in higher than normal tidal ranges.

Key Concept: Basic Concepts

c) Lunar cycles

[Solution Description] Ocean currents are primarily influenced by solar heating, wind, gravity, and the Coriolis force. Temperature and salinity also play significant roles. Among the options provided, lunar cycles mainly affect tides and not ocean currents.

Key Concept: Basic Definition

c) Coriolis force

[Solution Description] The Coriolis force is responsible for deflecting ocean currents to the right in the Northern Hemisphere due to Earth’s rotation.

Key Concept: Types of Fog

d) Evaporation fog

[Solution Description] When cold air moves over warmer water, the moisture in the air readily condenses upon contact with the warmer surface, resulting in evaporation fog.

Key Concept: Basic Concept

d) Wind

[Solution Description] Ocean currents are mainly influenced by solar energy, wind, gravity, and coriolis force. Among these, wind is considered a major driving force as it directly affects the movement of water on the surface.

Key Concept: Coriolis Force

c) Deflects them to the left

[Solution Description] The Coriolis force causes the deflection of moving objects such as wind and ocean currents. In the Southern Hemisphere, this deflection occurs to the left due to Earth’s rotation.

Key Concept: Current Classification

b) Cold current

[Solution Description] Cold ocean currents are usually found along the west coasts of continents in low and middle latitudes due to the upwelling of deeper, colder waters. This phenomenon is often associated with the general circulation pattern of ocean currents.

Key Concept: Wave Basics

b) Crest

[Solution Description] The highest point of a wave is known as the crest.

Key Concept: Tidal Mechanics

c) Centrifugal force

[Solution Description] The tidal bulge on the side of the Earth that is opposite to the moon is primarily caused by centrifugal force. This occurs because the gravitational pull of the moon causes the Earth and its water to be pulled towards it, creating a bulge on one side. On the opposite side, the centrifugal force resulting from the Earth-moon system rotating around their common center of mass leads to another bulge.

Key Concept: Perigee and Apogee Effects

b) Tidal ranges are less than average

[Solution Description] At apogee, the moon is farthest from the Earth, reducing its gravitational pull on the oceans. This results in a smaller tidal range than average because the difference between high tide and low tide will be less pronounced.

Key Concept: Tidal Types

b) Diurnal tide

[Solution Description] A diurnal tide is characterized by having one high tide and one low tide each day. This pattern typically occurs in certain areas where the tidal cycles are influenced primarily by local geographical factors.

Key Concept: Wave Motion

b) Circular

[Solution Description] Beneath the surface, water particles generally move in circular orbits as the wave passes. This type of motion is due to the orbital path followed by the particles when influenced by the wave energy.

Key Concept: Basic Definition

b) Gravitational pull of the sun and moon

[Solution Description] Tides are the periodic rise and fall of sea levels, which are primarily caused by the gravitational pull of the sun and moon on the Earth’s oceans.

Key Concept: Basic Classification

c) They occur in the upper 400 m of ocean water.

[Solution Description] Surface currents are ocean currents that occur in the upper 400 meters of the ocean’s water column and account for about 10\% of all ocean water. They are primarily influenced by prevailing winds and the Coriolis force.

Key Concept: Current Classification

c) Cold and warm currents

[Solution Description] Ocean currents can be classified based on temperature into two main categories: warm currents, which bring warmer water from equatorial regions, and cold currents, which carry colder water from polar regions.

Key Concept: Basic Definition

b) The sun and moon’s gravitational forces act in opposite directions

[Solution Description] Neap tides occur when the gravitational forces of the sun and moon counteract each other, which minimizes the overall effect on Earth’s tides, leading to the lowest tidal range.

Key Concept: Primary Forces Influencing Currents

c) Coriolis force

[Solution Description] The Coriolis force, resulting from the Earth’s rotation, influences the direction of ocean currents by causing them to deflect to the right in the northern hemisphere and to the left in the southern hemisphere.

Key Concept: Gravitational Forces

c) It exerts gravitational force creating one high and one low tide daily.

[Solution Description] The moon exerts a gravitational force on Earth’s oceans, creating tidal bulges. As the Earth rotates, different locations experience varying levels of this gravitational pull, resulting in diurnal patterns with one high tide and one low tide per day.

Key Concept: Tidal Forces

d) Moon

[Solution Description] The Moon’s gravitational pull has the most significant impact on Earth’s tides as it causes the regular rise and fall of sea levels known as tidal bulges.

Key Concept: Basic Definition

b) Wind

[Solution Description] The primary forces that influence ocean currents include solar energy, wind, gravity, and the Coriolis force. Among these, wind is the main driving factor for most surface ocean currents.

Key Concept: Tidal Height

c) It increases

[Solution Description] When the sun, moon, and earth are aligned, spring tides occur, resulting in higher tidal heights due to combined gravitational forces.

Key Concept: Tidal Terminology

a) Ebb

[Solution Description] The term “ebb” refers to the period when the tide is receding from the highest point (high tide) to the lowest point (low tide).

Key Concept: Tidal Calculation

b) 2/3 m/hour

[Solution Description] The rate of tide rise can be calculated by dividing the total tidal bulge by the number of hours.

$\text{Rate of tide rise} = \frac{\text{Total tidal bulge}}{\text{Hours}}$

$\text{Rate of tide rise} = \frac{4 \text{ meters}}{6 \text{ hours}} = \frac{2}{3} \text{ m/hour}$

Key Concept: Temperature Influence

a) East

[Solution Description] Warm currents are usually found on the eastern coast of continents in low and middle latitudes due to the way prevailing winds and the Coriolis effect direct their flow.

Key Concept: Frequency Types

b) Semi-diurnal tide

[Solution Description] In a semi-diurnal tide, there are usually two high tides and two low tides of approximately equal size every lunar day.

Key Concept: Tide Frequency Comparison

c) Semi-diurnal tide

[Solution Description] A semi-diurnal tide is characterized by having two high tides and two low tides each day. The heights of these successive tides are roughly the same. This feature distinguishes them from diurnal tides, which have only one high tide and one low tide per day, and mixed tides, which show significant variations in height.

Key Concept: Tidal Patterns

b) Spring tide

[Solution Description]

The type of tide described is known as a spring tide. Spring tides occur during full moons and new moons when the sun, moon, and earth are aligned, causing the gravitational forces to combine to produce higher high tides and lower low tides.

Key Concept: Gravitational Influence

c) Moon

[Solution Description]

The moon’s gravitational pull is primarily responsible for the creation of tides on Earth. It exerts a strong gravitational force that leads to the formation of tidal bulges on both the side facing the moon and the opposite side.

Key Concept: Ebb and Flow

a) Ebb

[Solution Description] The ebb is the period when the tide goes out and the water level falls between high tide and low tide, contrasting with the flow or flood tide when water rises.

Key Concept: Basic Concepts

b) Warm current

[Solution Description] Warm currents move from the equator towards the poles because they transfer heat from warmer to cooler areas.

Key Concept: Basic Definition

c) Trough

[Solution Description] The lowest point of a wave is known as the trough. This is where the displacement of the medium is at its minimum.

Key Concept: Tidal Calculation

c) 0.833 meters per hour

[Solution Description] The tidal range given is 10 meters, and it takes 12 hours for this change to occur. To find the average rate of change per hour, we use the formula:

$\text{Average Rate} = \frac{\text{Total Change in Water Level}}{\text{Time Taken}}$

Substituting the given values:

$\text{Average Rate} = \frac{10 \text{ meters}}{12 \text{ hours}} \approx 0.833 \text{ meters per hour}$

Thus, the average rate of change of water level per hour is approximately 0.833 meters.

Key Concept: Cold vs Warm

a) From equator to poles

[Solution Description] Warm-water currents travel from the equator along the surface towards the poles. This directional movement is a basic understanding of warm-water currents based on their nature and purpose to distribute heat.

Key Concept: Effects

c) By changing temperature and precipitation patterns

[Solution Description] Ocean currents transport heat, thereby affecting temperature and precipitation patterns along coastlines. Warm currents can raise temperatures while cold currents can lead to cooler climates.

Key Concept: Basic Terms

c) Trough

[Solution Description] The lowest point of a wave is known as the trough. This is in contrast to the highest point, which is called the crest.

Key Concept: Tidal Types

d) Diurnal tide

[Solution Description] A diurnal tide is a pattern where there is exactly one high tide and one low tide in a 24-hour period.

Key Concept: Temperature Effects

b) Cold

[Solution Description] According to the syllabus, the California Current has cold temperature characteristics as it is categorized as a cold current.

Key Concept: Basic Definitions

a) Crest

[Solution Description] The highest point of a wave is known as the crest. This corresponds to the maximum upward displacement in a wave pattern.

Key Concept: Basic Definition

c) Wind

[Solution Description] Ocean waves are mainly created by wind as it transfers energy to the water surface, causing the wave formation.

Key Concept: Definition Recall

c) When the sun, moon, and earth form a straight line

[Solution Description] Spring tides occur when the sun, moon, and earth are in a straight line. This alignment causes significant gravitational pull on Earth’s water, resulting in higher tides.

Key Concept: Basic Concepts

b) Warm currents

[Solution Description] Warm ocean currents raise the temperature of coastal areas by transporting heat from the equator towards the poles. This transport increases air temperatures over land, often leading to milder climates.

Key Concept: Tidal Types

a) Diurnal tide

[Solution Description] A diurnal tide is characterized by having just one high tide and one low tide in a 24-hour period.

Key Concept: Temperature Effects

c) Warm and rainy

[Solution Description] Warm ocean currents increase the temperature and humidity of the air above them, often resulting in warm and rainy climates along the east coasts of continents in tropical regions.

Key Concept: Economic and Trade Importance

c) Ocean currents reduce transportation costs by aiding navigation.

[Solution Description] Ocean currents help to reduce the time and fuel consumption for shipping by providing natural pathways that vessels can follow, leading to faster travel times.

Key Concept: Comparative Analysis

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] During apogean tides, the moon is farthest from Earth, reducing its gravitational pull on Earth’s oceans. This reduction in gravitational force leads to smaller tidal bulges, resulting in a tidal range that is below average. Hence, both the assertion and reason are true, and the reason correctly explains the assertion.

Key Concept: Density and Mobility

b) It causes the water to sink

[Solution Description] Dense water tends to sink below less dense water due to gravitational force. The increased density, often caused by higher salinity or lower temperature, causes the water mass to become heavier and sink, thus affecting its vertical mobility.

Key Concept: Current and Monsoonal Influence, Current and Marine Ecosystems

c) There are significant increases in productivity during and after monsoon seasons.

[Solution Description] Monsoon winds can reverse or alter ocean current directions, influencing the distribution of nutrients and plankton blooms. This variation can lead to seasonal peaks in marine productivity, supporting diverse marine species and enhancing the ecological balance during specific times of the year.