HBSE Class 10 Science Question Paper 2021 Answer Key
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Subjective Questions
Q1. On what factors does the resistance of a conductor depend ?
Ans. Resistance of a conductor depend on :
(i) Length of the wire
(ii) Area of cross-section of the wire
(iii) Nature of material of the wire.
Q2. Find the focal length of a lens of power +2.0D. What type of lens is this ? Write one use of this lens.
Ans. P=1/F, F=1/P = 1/2 = + 0.5 m
Uses of Convex Lens : It is use in microscopes and magnifying glasses to subject all the light to a specific point. It is use as a camera lens in cameras as they focus light for a clean picture. It is use in the correction of hypermetropia.
Q3. Explain principle and working of an electric motor by drawing a labelled diagram.
Ans. Principle– An electric motor is a rotating device that converts electrical energy to mechanical energy working.
Working– Current in the coil ABCD enters from the source battery through conducting brush X and flow back to the battery through brush Y. Notice that the current in the arm AB of the coil flows from A to B. In arm CD it flows from C to D that is opposite to the direction of current through arm AB on applying Fleming’s left hand rule for the direction of force on a current-carrying conductor in a magnetic field. We find that the force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards. Thus the coil and the Axle O, mounted free to turn about an axis, rotate anti-clockwise at half rotation. Q makes contact with the brush X and P with brush Y. Therefore the current in the coil gets reversed and flows along the path DCBA. The reversal of current also reverses the direction of force acting on the two arms AB and CD. Thus the arm AB of the coil that was earlier pushed down, is now pushed up and the arm CD previously pushed up is pushed down. There is a continuous rotation of the coil and to the axle.
OR
(a) Draw the magnetic lines of force around a bar magnet.
Ans.
(b) What is Fleming’s left hand rule ? Explain.
Q4. Fat and oil containing foods are packed with which gas and why ?
Ans. Oil and fat containing food items are flushed or surrounded with an inert gas such as Nitrogen while packing them to prevent their contact with oxygen present in the air. This is done to avoid rancidity of fats and oils.
Q5. Write common name and two uses of NaHCO3.
Ans. Common name of NaHCO3 is Baking Soda.
Uses of Baking Soda : Reduces the acidity in the stomach. It is acts as an antacid which is used to treat stomach upset and indigestion. It is used in the process of washing as a water softener. Due to the formation of soapy foam, it is used in fire extinguishers.
Q6. (a) How does atomic size vary in a group ? Explain.
Ans. Atomic size is the distance between the center of nucleus and the outermost electron in the outer shell. Across a period from left to right there is decrease in atomic size with increase in nuclear charge of the element. Atomic size increases down the group because of addition of extra shell.
(b) Explain Dobereiner’s law of Triads with one example.
Ans. According to Dobereiner’s law of triads, when elements are arranged in increasing order of their atomic masses, a group of three elements with similar chemical properties is obtained. This group is called a triad. The atomic mass of the middle element is equal to the arithmetic mean of the atomic masses of the other two elements. For example, the set of elements: calcium (Ca), strontium (Sr) and barium (Ba), with atomic masses 40, 88 and 137 respectively form a triad because they have similar chemical properties, and the atomic mass of strontium is approximately equal to the average of the atomic masses of calcium and barium. Arithmetic mean of atomic masses of calcium and barium = (40+137)/2 = 88.5
OR
(a) Name three elements whose valence shell contains one electron.
Ans. Lithium, Sodium, and Potassium
(b) What were the criteria used by Mendeleev in creating his periodic table ?
Ans. Elements are arranged in increasing order of their Atomic mass. Similarity of chemical properties (which he selected as the important factor in arranging elements). i.e. the element with similar chemical properties should be in the same group.
Q7. How is the process of pollination different from fertilization ?
Ans. Pollination– The process of transfer of pollen from the male parts (anther) of a flower to the female part (stigma) of the same or different flower is called pollination. It is an external mechanism and takes place on the outer part of a flower. Pollination occurs in flowering plants only. It has two types: Self-pollination, Cross-pollination. No formation of pollen tube. Pollination takes place before fertilization.
Fertilization– Fertilization is the common process, involving the union of the male gamete (sperm) and female gamete (egg). It is an internal mechanism and takes place inside the flowers. Fertilization is followed by almost every plant and living being present on earth. It has No types. Formation of pollen tube which helps in transferring of male gametes up to an egg cell. Fertilization takes place after pollination.
Q8. Describe three different methods of contraception.
Ans. Natural Method– It involves avoiding the chances of meeting of sperms and ovum. In this method, the sexual act is avoided from day 10th to 17th of the menstrual cycle because, during this period, ovulation is expected and therefore, the chances of fertilization are very high.
Barrier Method– In this method, the fertilization of ovum and sperm is prevented with the help of barriers. Barriers are available for both males and females. Condoms are barriers made of thin rubber that are used to cover penis in males and vagina in females.
Oral Contraceptives– In this method, tablets or drugs are taken orally. These contain small doses of hormones that prevent the release of eggs and thus fertilization cannot occur.
Implants and Surgical Methods– Contraceptive devices such as the loop or Copper-T are placed in the uterus to prevent pregnancy. Some surgical methods can also be used to block the gamete transfer. It includes the blocking of vas deferens to prevent the transfer of sperms known as vasectomy. Similarly, fallopian tubes of the female can be blocked so that the egg will not reach the uterus known as tubectomy.
Q9. (a) Draw a well labelled diagram of Human Excretory System.
Ans.
(b) What are the differences between transport of Materials in xylem and phloem ?
Ans. Xylem– Xylem transports soluble minerals and water molecules. Water is absorbed by the roots and is transported to the aerial parts of the plant like the stem and leaves. Xylem tissues are composed mainly of dead cells. Transportation in the xylem is unidirectional from roots to leaves. Xylem provides mechanical strength to the plant.Xylem is responsible for the amount of water loss through transpiration and photosynthesis. Xylem consists of tracheids, vessels, parenchyma, and fibers.
Phloem– Phloem transports food and other nutrients like sugar and amino acids. Food is formed in the leaves from where it is transported to the storage organs and the growing parts of the plants. Phloem tissues are mainly composed of living cells. Phloem transportation is bidirectional from leaves to various plant parts. Phloem transports the sugar in the storage organs. Phloem is responsible for transporting proteins and mRNAs throughout the plant. Phloem consists of sieve tubes, companion cells, parenchyma, fibers.
OR
(a) What are the differences between aerobic and anaerobic respiration ?
Ans. Aerobic Respiration– Oxygen is required for this type of respiration to take place. It involves the exchange of gases between the organism and the outside environment. Process of respiration takes place in the cytoplasm and the mitochondria. Glucose breaks down or complete oxidation into carbon dioxide and water. All higher organisms such as mammals perform this type of respiration.
Anaerobic Respiration– No requirement of oxygen in this process. Exchange of gases is there but oxygen gas does not take part.