Class 7 General Science NCERT Based - 2 - Free MCQ Practice Test with solutions,

• Heat Transfer: The movement of heat from a warmer object to a colder one – when two substances at different temperatures are mixed together, heat flows from the warmer body to the cooler body until they reach the same temperature (Zeroth Law of

• Thermodynamics – Thermal Equilibrium). Part of the heat lost by the warmer body is transferred to the cooler body and part is lost to the surrounding object or the air.

• Convection is the process of heat transfer by the bulk movement of molecules within fluids such as gases and liquids. The initial heat transfer between the object and the fluid takes place through conduction, but the bulk heat transfer happens due to the motion of the fluid.

  • Convection is the process of heat transfer in fluids by the actual motion of matter.

  • It happens in liquids and gases.

  • It may be natural or forced.

  • It involves a bulk transfer of portions of the fluid.

• Conduction is the transfer of energy in the form of heat or electricity from one atom to another within an object by direct contact. Conduction occurs in solids, liquids, and gases. However, solids transfer energy most efficiently since the molecules in solids are most tightly packed, and the molecules are closer together, as shown in this figure. For liquids and gases, the density of the particles are generally lower than those of solids and the particles are farther apart, so the energy transfer is less efficient.

To match List I to List II and select the correct answer, let's analyze each pair:

- A. Time at which land breeze flows: Land breeze typically flows at night (because the land cools faster than the sea, causing the air to move from the land to the sea).
- B. Time at which sea breeze flows : Sea breeze typically flows at day (because the land heats up faster than the sea, causing the air to move from the sea to the land).
- C. Dark-colored clothes : Dark-colored clothes are generally worn more in the winter season because they absorb more heat.
- D. Light-colored clothes: Light-colored clothes are generally worn more in the summer season because they reflect more heat and keep the body cooler.

So, the correct matching is:
- A - 4
- B - 3
- C - 2
- D - 1

Explanation:

Fahrenheit and Kelvin: In the Fahrenheit scale, water freezes at 32°F and boils at 212°F. In the Kelvin scale, water freezes at 273.15 K and boils at 373.15 K. The two scales have different zero points and step sizes, so they can never give equal numerical values for the temperature of a body.

Celsius and Kelvin: The Celsius scale has water freezing at 0°C and boiling at 100°C, while the Kelvin scale has water freezing at 273.15 K and boiling at 373.15 K. Since the Kelvin scale starts at absolute zero (which is -273.15°C), it is impossible for the two scales to have equal numerical values for any temperature.

Kelvin and Platinum: Platinum here refers to the Platinum Resistance Thermometer (PRT), which is a temperature measurement device that uses the relationship between electrical resistance and temperature. It doesn't have a scale of its own, instead, it is used to measure temperature in Celsius, Fahrenheit, or Kelvin. Therefore, it is not possible to compare Kelvin and Platinum directly.

These substances taste sour because they contain acids, whereas the substances which are bitter in taste and feel soapy on touch are known as bases. The names of some major acids and related substances are: Name of acid Found in

1. Acetic acid Vinegar

2. Formic acid Ant’s sting

3. Citric acid Citrus fruits such as oranges, lemons, etc.

4. Lactic acid Curd

5. Oxalic acid Spinach

6. Ascorbic acid Amla, Citrus fruits (Vitamin C)

7. Tartaric acid Tamarind, grapes, unripe mangoes, etc. All the acids mentioned above occur in nature.

Name of base Found in

1. Calcium hydroxide : Lime water

2. Ammonium hydroxide : Window cleaner

3. Sodium hydroxide/Potassium hydroxide: Soap

4. Tartaric acid: grapes, bananas, tamarinds, and citrus

• Neutral solution is a solution whose pH is close to 7. They prefer remaining at a perfect balance.Usually a neutral solution is neither acidic nor basic. It doesn't imply that the neutral solution lacks charged ions.

• Natural Indicator is a type of indicator that can be found naturally and can determine whether the substance is an acidic substance or a basic substance. Some examples of natural indicators are red cabbage, turmeric, grape juice, turnip skin, curry powder, cherries, beetroots, onion, tomato, etc.

• Acid rain, or acid deposition, is a broad term that includes any form of precipitation with acidic components, such as sulfuric or nitric acid that fall to the ground from the atmosphere in wet or dry forms. This can include rain, snow, fog, hail or even dust that is acidic.

• Acid rain results when sulfur dioxide (SO₂) and nitrogen oxides (NOX) are emitted into the atmosphere and transported by wind and air currents. The SO₂ and NOX react with water, oxygen and other chemicals to form sulfuric and nitric acids. These then mix with water and other materials before falling to the ground.

• While a small portion of the SO₂ and NOX that cause acid rain is from natural sources such as volcanoes, most of it comes from the burning of fossil fuels.

• The wastes of many factories contain acids. If they are allowed to flow into the water bodies, the acids will kill fish and other organisms. The factory wastes are, therefore, neutralised by adding basic substances.

• Our stomach contains hydrochloric acid. It helps us to digest food. But too much acid in the stomach causes indigestion, which is painful. To relieve indigestion, we take an antacid such as milk of magnesia, which contains magnesium hydroxide. It neutralises the effect of excessive acid.

• When an ant bites, it injects the acidic liquid (formic acid) into the skin. The effect of the acid can be neutralised by rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution, which contains zinc carbonate.

In tearing of paper, it had undergone changes in size. Properties such as shape,size,colour,state of a substance are called physical properties. A change in which a substance undergoes a change in its physical properties is called a physical change. Rest, other changes are the examples of chemical change.

• Physical changes: Changes in the Physical Properties of a Substance are known as Physical Changes. Physical Properties of a Substance include colour, size, shape, state, temperature, odour, appearance, texture and many more.

• In addition, Physical Changes do not lead to the formation of new substances. Physical Changes may or may not be reversible. Examples of Physical Change

  • Breaking/Crushing of any Object

  • Expansion of Metal on Heating

  • Dissolving Sugar or Salt (Solute) in Water (Solvent) (as a result, a solution is formed)

  • Solidification of Molten Metal on Cooling

  • Shredding Paper

• Chemical Changes: One or more substances, at times, react with one another or substances which are readily available in the environment. This consequently leads to the formation of a new substance(s). The formation of the new substance can also be accompanied by one or more of the following:

  1. Emission of Heat (Exothermic Reaction) as a result of a Chemical Changes

  2. Absorption of Heat (Endothermic Reaction) as a result of a Chemical Changes

  3. Emission Light as a result of a Chemical Changes

  4. Production of Sound as a result of a Chemical Changes

  5. Change or emission of Odour as a result of a Chemical Changes

  6. Emission of Gas as a result of a Chemical Changes

• Exothermic reactions are reactions or processes that release energy, usually in the form of heat or light. In an exothermic reaction, energy is released because the total energy of the products is less than the total energy of the reactants.

• For this reason, the change in enthalpy, [latex]\Delta H[/latex], for an exothermic reaction will always be negative. In the presence of water, a strong acid will dissociate quickly and release heat, so it is an exothermic reaction.

• Endothermic reactions are reactions that require external energy, usually in the form of heat, for the reaction to proceed. Since endothermic reactions draw in heat from their surroundings, they tend to cause their environments to cool down.

• They are also generally non-spontaneous, since endothermic reactions yield products that are higher in energy than the reactants. As such, the change in enthalpy for an endothermic reaction is always positive. In order to melt the ice cube, heat is required, so the process is endothermic.

• Galvanizing, protection of iron or steel against exposure to the atmosphere and consequent rusting by application of a zinc coating. Properly applied, galvanizing may protect from atmospheric corrosion for 15 to 30 years or more.

• As discontinuities or porosity develop in the coating, galvanic or electrolytic action ensues; the iron or steel, however, is protected by sacrificial corrosion, a phenomenon in which, as long as the zinc and the iron are in contact, atmospheric oxidation spares the iron and affects the zinc.

• Acid, any substance that in water solution tastes sour, changes the colour of certain indicators (e.g., reddens blue litmus paper), reacts with some metals (e.g., iron) to liberate hydrogen, reacts with bases to form salts, and promotes certain chemical reactions (acid catalysis).

• Examples of acids include the inorganic substances known as the mineral acids—sulfuric, nitric, hydrochloric, and phosphoric acids—and the organic compounds belonging to the carboxylic acid, sulfonic acid, and phenol groups.

• Acids may be identified as either strong or weak acids based on how completely they dissociate into their ions in water.

• A strong acid, such as hydrochloric acid, completely dissociates into its ions in water.

• A weak acid only partly dissociates into its ions, so the solution contains water, ions, and the acid (e.g., acetic acid).

• Weather is the day-to-day state of the atmosphere, and its short-term variation in minutes to weeks. People generally think of weather as the combination of temperature, humidity, precipitation, cloudiness, visibility, and wind. Climate is the weather of a place averaged over a period of time, often 30 years.

• Climate information includes the statistical weather information that tells us about the normal weather, as well as the range of weather extremes for a location.

• The polar regions present an extreme climate. These regions are covered with snow and it is very cold for most part of the year.

• For six months the sun does not set at the poles while for the other six months the sun does not rise.

• In winters, the temperature can be as low as –37°C. Animals living there have adapted to these severe conditions.Birds migrate to warmer regions when winter sets in. They come back after the winter is over.

• The tropical region has generally a hot climate because of its location around the equator. Even in the coldest month the temperature is generally higher than about 15°C. During hot summers, the temperature may cross 40°C.

• Days and nights are almost equal in length throughout the year. These regions get plenty of rainfall.

• An important feature of this region is the tropical rainforests. Tropical rainforests are found in Western Ghats and Assam in India, Southeast Asia, Central America and Central Africa.

• The lion-tailed macaque (also called Beard ape) lives in the rainforests of Western Ghats. Its most outstanding feature is the silver-white mane, which surrounds the head from the cheeks down to its chin. It is a good climber feeds mainly on fruits, seeds, young leaves, stems, flowers and buds. This beard ape also searches for insects under the bark of the trees. Since it is able to get sufficient food on the trees, it rarely comes down on the ground.

• Wind is the movement of air caused by the uneven heating of the Earth by the sun. It does not have much substance—you cannot see it or hold it—but you can feel its force.

• Warm equatorial air rises higher into the atmosphere and migrates toward the poles. This is a low-pressure system.

• At the same time, cooler, denser air moves over Earth’s surface toward the Equator to replace the heated air. This is a high-pressure system. Winds generally blow from high-pressure areas to low-pressure areas. The boundary between these two areas is called a front.

• The complex relationships between fronts cause different types of wind and weather patterns. Prevailing winds are winds that blow from a single direction over a specific area of the Earth.

• The Sun's rays are straight at the equator, so the areas around the equator receive maximum heat. The warm air rises, and the cooler air from the regions in the 0–30 degrees latitude belt on either side of the equator moves in.

• These winds blow from the north and the south towards the equator. At the poles, the air is colder than that at latitudes about 60 degrees.

• The warm air at these latitudes rises up and the cold wind from the polar regions rushes in, to take its place. In this way, wind circulation is set up from the poles to the warmer latitudes.

1. In winter, the wind flows from the land to the ocean:
   This is true because during winter, the land cools down faster than the ocean, creating high-pressure areas on the land and low-pressure areas over the ocean. The wind flows from high-pressure areas to low-pressure areas, i.e., from land to ocean.

2. In summers, the wind flows from the oceans towards the land:
   This is true because in summer, the land heats up more quickly than the ocean, creating low-pressure areas on land and high-pressure areas over the ocean. As a result, winds flow from the oceans towards the land, bringing moisture.

3. The winds from the oceans carry water vapour and bring rain. It is a part of the water cycle:
   This is true as these oceanic winds, known as monsoon winds, are rich in water vapour. When they reach land and rise, they cool and condense, bringing rain. This process is integral to the water cycle.

Thus, all three statements are correct.Therefore,Correct Answer- Option D

• These winds carry water droplets upwards, where they freeze, and fall down again. The swift movement of the falling water droplets along with the rising air create lightning and sound. It is this event that we call a thunderstorm.

• The centre of a cyclone is a calm area. It is called the eye of the storm. A large cyclone is a violently rotating mass of air in the atmosphere, 10 to 15 km high. The diameter of the eye varies from 10 to 30 km.

• It is a region free of clouds and has light winds. Around this calm and clear eye, there is a cloud region of about 150 km in size. In this region there are high-speed winds (150–250 km/h) and thick clouds with heavy rain. Away from this region the wind speed gradually decreases. The formation of a cyclone is a very complex process.

• India's coast is extremely vulnerable to cyclones. With a coastline of 7517 km, the country is exposed to nearly 10 percent of the world's tropical cyclones.

• Although cyclones affect the entire coast of India, the eastern coast is significantly more prone to cyclones as compared to the western coast.

• The East coast of India faces the Bay of Bengal while the west coast of India is situated on the shores of Arabian Sea.

• It is called a ‘hurricane’ in the American continent. In the Philippines and Japan it is called a 'typhoon'

• A tropical cyclone is a storm system, characterised by a low-pressure centre surrounded by a spiral arrangement of thunderstorms that produce strong winds and heavy rain.

• A characteristic feature of tropical cyclones is the eye, a central region of clear skies, warm temperatures, and low atmospheric pressure.

• Typically, atmospheric pressure at the surface of Earth is about 1,000 millibars. At the centre of a tropical cyclone, however, it is typically around 960 millibars, and in a very intense “super typhoon” of the western Pacific it may be as low as 880 millibars.

• In addition to low pressure at the centre, there is also a rapid variation of pressure across the storm, with most of the variation occurring near the centre.