CBSE Class 7 Science Revision Worksheet Set 13

PHYSICS

Q1. Choose and write only the correct option.
i) Light passes through ________ completely.
(a) Frosted glass
(b) Card board
(c) Plain glass
(d) Butter paper
Answer: (c) Plain glass
Transparent materials like plain glass allow light to pass through them completely without scattering.
In simple words: Plain glass is transparent, so light goes right through it.

Exam Tip: Remember the three types of materials: transparent (allows light completely), translucent (allows partially), and opaque (does not allow light).

ii) An MCB can be used in place of ________
(a) A bulb
(b) A fuse
(c) An electric iron
(d) An Electric bell
Answer: (b) A fuse
An MCB (Miniature Circuit Breaker) automatically switches off when current in the circuit exceeds the safe limit, serving the same protective purpose as an electric fuse.
In simple words: An MCB protects circuits from overloading just like a fuse does.

Exam Tip: MCBs are reusable safety devices, whereas traditional wire fuses melt and need replacement after a fault.

iii) A solenoid is -
(a) Similar to electromagnet
(b) Weaker than electromagnet
(c) Stronger than electromagnet
(d) Not an electric appliance
Answer: (a) Similar to electromagnet
A coil of insulated wire wound in the shape of a cylinder is called a solenoid, which behaves like a magnet when electric current flows through it.
In simple words: A current-carrying coil of wire acts just like an electromagnet.

Exam Tip: Inserting a soft iron core inside a solenoid turns it into a powerful electromagnet.

Q2. What do you mean by rectilinear propagation of light?
Answer: The property of light traveling in a straight line in a homogenous transparent medium is known as the rectilinear propagation of light.
In simple words: Light always travels in a straight line.

Exam Tip: Mention pinhole cameras or beam of sunlight through a gap as classic examples demonstrating this property.

Q3. Draw a neat diagram to show regular reflection.
Answer: Regular reflection takes place when parallel rays of light fall on a smooth and polished surface, and the reflected rays are also parallel to each other.
In simple words: Smooth surfaces bounce light back in one specific direction orderly.

Exam Tip: Always draw arrowheads on ray lines to indicate the direction of light travel.

Q4. Name the effect on which an electric bell works.
Answer: An electric bell works on the magnetic effect of electric current.
In simple words: It works using electromagnetism.

Exam Tip: Be precise; do not write heating effect or chemical effect.

Q5. Can you measure the wind speed? If yes, then name the instruments used for it. If not then why?
Answer: Yes, wind speed can be measured. The instrument used to measure wind speed is called an anemometer.
In simple words: Yes, we use an anemometer to measure how fast the wind blows.

Q6. Which of the following is strictly prohibited during cyclones?
(a) Use of landline phones
(b) Parking of cars near trees
(c) Listen to radio for weather update
(d) Storing drinking water for emergencies
Answer: (a) Use of landline phones
Electrical switches, landline phones connected to outside wires, and metal objects can conduct lightning or suffer electrical hazards, though wired landlines are generally risky during severe lightning/storms. However, parking under trees is dangerous due to falling branches. Wait, landline phones with metallic wires can be hazardous during thunderstorms/cyclones associated with lightning, but let's evaluate standard safety rules: Do not touch electrical appliances connected to wires. Actually, cordless or mobile phones are safe, but wired landlines connected to external lines can transmit electrical surges.
In simple words: Avoid using wired landline phones during severe storms with lightning.

Exam Tip: Always prioritize safety guidelines issued by meteorological departments during disasters.

Q7. Give reason.
i) During thunderstorm avoid going close to a metallic object.
Answer: Metals are good conductors of electricity. During a thunderstorm, lightning carries a massive electrical charge and can easily strike tall metallic objects, posing a severe electrocution hazard to anyone nearby.
In simple words: Metals conduct electricity and can attract lightning strikes.

Exam Tip: Always stay away from poles, metal fences, and open vehicles during lightning.

ii) Centre of cyclone is calm.
Answer: The center of a cyclone is called the eye, which is a region of calm weather with light winds and clear or partly cloudy skies because descending air suppresses cloud formation in that specific core area.
In simple words: The eye at the center has very low pressure and calm weather.

Exam Tip: Remember that the eye is surrounded by a violent region of high-speed winds and heavy rain known as the eyewall.

Q8. Differentiate between concave lens and convex lens along with a suitable diagram of both.
Answer:
1. Convex Lens: Thicker in the middle and thinner at the edges; converges light rays.
2. Concave Lens: Thinner in the middle and thicker at the edges; diverges light rays.
In simple words: Convex lenses bend light inward (magnifying), while concave lenses bend light outward.

Exam Tip: Convex is converging (like cave-in edges vs bulging middle); Concave curves inward like a cave.

CHEMISTRY

Q9. Choose and write only the correct option.
i) Rainwater that does not seep into the ground but runs off on the surface is called -
(a) Water table
(b) Surface water
(c) Frozen water
(d) Water cycle
Answer: (b) Surface water
Water flowing over the surface of the land without infiltrating the soil is termed surface runoff or surface water.
In simple words: Water flowing on the ground surface is surface water.

Exam Tip: Surface water feeds rivers, lakes, and oceans.

ii) The formula of rust is -
(a) \(\text{Fe}_2\text{O}_3\)
(b) \(\text{FeO}\)
(c) \(\text{Fe}_3\text{O}_4\)
(d) \(\text{Fe}_2\text{O}_3 \cdot x\text{H}_2\text{O}\)
Answer: (d) \(\text{Fe}_2\text{O}_3 \cdot x\text{H}_2\text{O}\)
Rust is hydrated iron(III) oxide formed by the reaction of iron with oxygen and moisture in the air.
In simple words: Rust is hydrated iron oxide containing water molecules.

Exam Tip: Always include the water of crystallization (\(x\text{H}_2\text{O}\)) when writing the chemical formula for rust.

iii) Which of the following is not caused by increase in population?
(a) Depletion of ground water
(b) Excessive consumption of water
(c) Conservation of water
(d) Decrease in infiltration
Answer: (c) Conservation of water
Population growth leads to higher water consumption, more construction (decreasing infiltration), and over-extraction of groundwater, whereas conservation is a protective measure, not a consequence of population increase.
In simple words: Conservation means saving water, which is done by humans, not caused by overpopulation.

Exam Tip: Read options carefully to distinguish between causes, effects, and remedial actions.

Q10. Write the number of nucleons present in Sulphur, which has 16 neutrons. Also, state its atomicity.
Answer:
Atomic number of Sulphur (\(S\)) = 16 (number of protons = 16).
Number of neutrons = 16.
Number of nucleons = Protons + Neutrons = \(16 + 16 = 32\).
Atomicity of Sulphur (commonly found as \(\text{S}_8\)) = 8.
In simple words: Sulphur has 32 nucleons (16 protons + 16 neutrons) and exists as 8 atoms per molecule (atomicity = 8).

Exam Tip: Nucleons refer to the total number of protons and neutrons in the nucleus.

Q11. Name the process (any two) that takes place in water cycle. Why is water cycle necessary for life?
Answer:
Processes in the water cycle: Evaporation and Condensation (or Transpiration and Precipitation).
Necessity: The water cycle maintains a continuous supply of fresh water on Earth, regulates climate, supports agriculture, and sustains all living organisms.
In simple words: Evaporation and condensation drive the water cycle, ensuring freshwater availability for survival.

Exam Tip: Mention key terms like evaporation, transpiration, condensation, and precipitation for full credit.

Q12. Write the numbers of atoms of each element present in -
i) Aluminium sulphate
ii) Magnesium bi carbonate
Answer:
i) Formula of Aluminium sulphate: \(\text{Al}_2(\text{SO}_4)_3\)
- Aluminium (Al) = 2 atoms
- Sulphur (S) = 3 atoms
- Oxygen (O) = 12 atoms
ii) Formula of Magnesium bicarbonate: \(\text{Mg(HCO}_3)_2\)
- Magnesium (Mg) = 1 atom
- Hydrogen (H) = 2 atoms
- Carbon (C) = 2 atoms
- Oxygen (O) = 6 atoms
In simple words: Multiply numbers outside brackets by subscripts inside brackets to find total atoms.

Exam Tip: Always derive the correct chemical formula using valencies before counting atoms.

Q13. Give reason.
i) Indian farmers depend upon ground water for irrigating their crops.
Answer: Monsoons in India are often erratic and unevenly distributed. Due to the lack of adequate perennial canal systems across all agricultural regions, farmers rely heavily on groundwater pumped through tube wells for irrigation.
In simple words: Erratic rainfall makes underground water essential for dependable crop irrigation.

Exam Tip: Mention monsoon dependency and inadequate canal irrigation networks as primary reasons.

ii) Inspite of being painted, ships get damaged.
Answer: Ships remain continuously immersed in saline sea water. Saltwater accelerates corrosion, and continuous abrasion by waves, marine life, and docking scrapes off the protective paint layer, exposing the iron hull to rust and damage.
In simple words: Constant exposure to salty seawater and friction wears off paint, causing rusting.

Exam Tip: Highlight the role of dissolved salts in seawater as corrosive agents.

Q14. Describe your observation for the reaction shown in the diagram. Define the type of reaction.
Answer: Observation: When an iron rod is dipped into a blue-coloured copper sulphate solution, the blue colour gradually fades to light green (due to formation of iron sulphate), and a brownish coating of copper metal gets deposited on the iron rod.
Type of reaction: Displacement reaction.
In simple words: Iron displaces copper from copper sulphate solution, turning the solution green and coating the iron with copper.

Exam Tip: Remember: More reactive metals displace less reactive metals from their salt solutions.

Q15. Translate into a balanced chemical equation.
i) Sodium metal is formed and chlorine gas is released by the electrolysis of sodium chloride.
ii) Potassium hydroxide and hydrochloric acid react together to give potassium chloride and water.
Answer:
i) \(2\text{NaCl (aq)} \xrightarrow{\text{electrolysis}} 2\text{Na (s)} + \text{Cl}_2\text{ (g)}\)
ii) \(\text{KOH (aq)} + \text{HCl (aq)} \rightarrow \text{KCl (aq)} + \text{H}_2\text{O (l)}\)
In simple words: Write correct chemical formulas for reactants and products and balance atoms on both sides.

Exam Tip: Always include physical states like (s), (l), (g), and (aq) where required.

Q16. Answer the following.
i) What is spring water?
Answer: Groundwater that naturally flows out to the earth's surface from an underground aquifer is called spring water.
In simple words: Natural underground water flowing out to the surface is spring water.

Exam Tip: Springs form when the water table intersects the ground surface.

ii) What are the advantages of rainwater harvesting?
Answer:
1. Recharges groundwater levels.
2. Overcomes water scarcity during dry seasons.
3. Reduces urban flooding and soil erosion.
4. Provides a sustainable supplementary source of clean water.
In simple words: Rainwater harvesting stores rainwater to recharge groundwater and fight water shortages.

Q17. Choose and write only the correct option.
i) The digestive juice that does not contain any enzyme is ________
(a) Bile juice
(b) Saliva
(c) Gastric juice
(d) Pancreatic juice
Answer: (a) Bile juice
Bile juice secreted by the liver does not contain any digestive enzymes; it helps in the emulsification of fats.
In simple words: Bile helps digest fats, but it contains no enzymes.

Exam Tip: Bile aids fat digestion by breaking large fat droplets into smaller ones.

ii) Which of the following is not a heterotroph?
(a) Cuscuta
(b) Nepenthes
(c) Algae
(d) Mistletoe
Answer: (c) Algae
Algae contain chlorophyll and perform photosynthesis to manufacture their own food, making them autotrophs.
In simple words: Algae make their own food through photosynthesis, so they are autotrophs.

Exam Tip: Autotrophs make food; heterotrophs depend on other organisms for nutrition.

iii) The end products of aerobic respiration are:
(a) \(\text{C}_6\text{H}_{12}\text{O}_6, \text{CO}_2\)
(b) \(\text{C}_2\text{H}_5\text{OH}, \text{CO}_2\)
(c) \(6\text{CO}_2, 6\text{H}_2\text{O}\)
(d) \(\text{C}_2\text{H}_5\text{OH}, 6\text{H}_2\text{O}\)
Answer: (c) \(6\text{CO}_2, 6\text{H}_2\text{O}\)
During aerobic respiration in the presence of oxygen, glucose breaks down completely into carbon dioxide and water with the release of energy.
In simple words: Aerobic respiration produces carbon dioxide, water, and energy.

Exam Tip: Remember: Aerobic = with oxygen (\(\text{CO}_2 + \text{H}_2\text{O}\)); Anaerobic = without oxygen (alcohol or lactic acid).

Q18. Name the respiratory organs of the following organisms.
i) Cockroaches
ii) Prawns
Answer:
i) Cockroaches: Tracheae (air tubes with spiracles)
ii) Prawns: Gills
In simple words: Cockroaches breathe through air tubes called tracheae, and prawns breathe through gills.

Q19. Write any two points of difference between inhalation and exhalation.
Answer:
1. Inhalation: Intake of oxygen-rich air into the lungs; ribs move upward and outward, and the diaphragm moves downward.
2. Exhalation: Release of carbon dioxide-rich air out of the lungs; ribs move downward and inward, and the diaphragm moves upward to its dome shape.
In simple words: Inhalation brings air in (diaphragm goes down), and exhalation pushes air out (diaphragm goes up).

Exam Tip: Contrast the movement of the ribcage and diaphragm clearly in both processes.

Q20. What is assimilation?
Answer: The process by which absorbed food nutrients are transported via the blood to different cells of the body to build complex substances like proteins required for growth and energy is called assimilation.
In simple words: Assimilation is the utilization of absorbed food by body cells for growth and repair.

Q21. How do the following glands help in digestion of food?
i) Liver
ii) Salivary glands
Answer:
i) Liver: Secretes bile juice, which helps break down (emulsify) fats into tiny droplets for easy digestion.
ii) Salivary Glands: Secretes saliva containing the enzyme amylase, which converts complex starch into simpler sugars.
In simple words: Liver bile digests fats, and salivary glands turn starch into sugar in the mouth.

Exam Tip: Note that liver produces bile (stored in gall bladder), while salivary glands produce saliva.

Q22. Write the function of each of the following.
i) Chlorophyll
ii) Rumen
Answer:
i) Chlorophyll: Traps solar energy (sunlight) necessary for plants to carry out photosynthesis.
ii) Rumen: A sac-like part of the stomach in ruminants where food is quickly swallowed and partially digested (forming cud) before being regurgitated for chewing.
In simple words: Chlorophyll captures sunlight for plants, and the rumen stores and partially digests food in grass-eating animals.

Q23. Select the odd one out and give reason.
Stomach, Guard cells, Xylem, Subsidiary cells
Answer:
Odd one out: Stomach.
Reason: Stomach is an organ of the human digestive system, whereas guard cells, xylem, and subsidiary cells are plant tissues/cells (stomata components and vascular tissue).
In simple words: Stomach is an animal organ, while the rest belong to plants.

Exam Tip: Always state the category of each item to clearly justify the odd one out.

Q24. Draw a well labelled diagram of:
i) Bread mould
ii) Human digestive system
iii) Human respiratory system
Answer:
i) Bread mould (Rhizopus): Consists of thread-like hyphae and erect sporangiophores bearing spore-containing sporangia at their tips.
ii) Human digestive system: Comprises buccal cavity, oesophagus, stomach, small intestine, large intestine, rectum, and anus, along with associated glands (liver, pancreas, salivary glands).
iii) Human respiratory system: Comprises nasal cavity, pharynx, trachea, bronchi, lungs, and diaphragm.
In simple words: Draw neat, proportional outlines and label all major anatomical parts clearly.

Exam Tip: Use sharp pencils and straight label lines that do not cross each other.