CBSE EXAMINATION PAPER-2023
SCIENCE
(Solved)
General Instructions :
Read the following instructions carefully and follow them :
- This question paper contains 46 questions. All questions are compulsory.
- This question paper is divided into 5 sections.
- Section A – questions number 1 to 3 are case based questions
- Section B – questions number 4 to 23 are multiple choice questions
- Section C – questions number 24 to 32 are very short answer
- Section D – questions number 33 to 42 are short answer
- Section E – questions number 43 to 46 are long answer
- There is no overall choice given in the question paper. However, an internal choice has been provided in few questions.
- Use of calculator is NOT allowed.
Section A
(1) What happens when copper is heated in air? Give the equation of the reaction involved.
[1 Mark](2) Why are some metal oxides categorized as amphoteric? Give one example.
[1 Mark](3) Complete the following equations: (i) Na₂O₍ₛ₎ + H₂O₍ₗ₎ → (ii) Al₂O₃ + 2 NaOH → ?
(4) On burning sulphur in oxygen a colourless gas is produced. (i) Write chemical equation for the reaction. (ii) Name the gas formed. (iii) State the nature of the gas. (iv) What will be the action of this on a dry litmus paper?
In order to trace the inheritance of traits Mendel crossed pea plants having one contrasting character or a pair of contrasting characters. When he crossed pea plants having round and yellow seeds with pea plants having wrinkled and green seeds, he observed that no plants with wrinkled and green seeds were obtained in the F₁ generation. When the F₁ generation pea plants were cross-bred by self-pollination, the F₂ generation had seeds with different combinations of shape and colour also.
(1) Differentiate between dominant and recessive traits.
[1 Mark](2) State the ratio of the combinations observed in the seeds of F₂ generation in the above case. What do you interpret from this result?
The ratio of combinations observed in the seeds of the F₂ generation was approximately 9:3:3:1. This means that out of 16 plants, 9 had round yellow seeds, 3 had round green seeds, 3 had wrinkled yellow seeds, and 1 had wrinkled green seeds. This result shows that the traits for seed shape and seed color assort independently of each other during inheritance. It also confirms Mendel's principle of independent assortment, which states that different traits are inherited separately and new combinations of traits can appear in the offspring.
Ratio of combinations in F2 is 9 round yellow : 3 round green : 3 wrinkled yellow : 1 wrinkled green - Traits of seed shape and color assort independently - Mendel's principle of independent assortment - Explanation that new combinations of traits are formed in F₂ generation
(3) Given below is a cross between a pure violet flowered pea plant (V) and a pure white flowered pea plant (v). Diagrammatically explain what type of progeny is obtained in F₁ generation and F₂ generation: Pure violet flowered plant × Pure white flowered plant. (V V) (v v)
(4) Write any two pairs of contrasting characteristics of pea plant used by Mendel other than those mentioned above.
Hold a concave mirror in your hand and direct its reflecting surface towards the sun. Direct the light reflected by the mirror on to a white card-board hold close to the mirror. Move the card-board bock and forth gradually until you find a bright, sharp spot of light on the board. Thik spot of light is the image of the sun on the sheet of paper, which is also termed as "Principal Focus" of the concave mirror.
(1) List two applications of concave mirror.
(2) If the distance between the mirror and the principal focus is 15 cm. find the radius of curvature of the mirror,
(3) Draw a ray diagram to show the type of image formed when an object is placed between pole and focus of n concave mirror.
(4) An object 10 cm in size is placed at 100 cm in front of a concave mirror. If its image is formed at the same point where the object is located, find: (i) focal length of the mirror, and (ii) magnification of the image formed with sign as per Cartesian sign convention.
Section B
In the experimental setup given below, it is observed that on passing the gas produced in the reaction in the solution 'X' the solution 'X' first turns milky and then colourless.
The option that justifies the above stated observation is that 'X' is aqueous calcium hydroxide and
The emission of brown fumes in the given experimental set-up is due to
MnO₂ + x HCl → MnCl₂ + y H₂O + z Cl₂
In order to balance the above chemical equation, the values of x, y and z respectively are:
The table below has information regarding pH and the nature (acidic/basic) of four different solutions. Which one of the options in the table is correct?
The correct option corresponds to the one that accurately matches pH values with the nature of the solutions. Acidic solutions have pH less than 7, basic solutions have pH greater than 7, and neutral solutions have pH equal to 7. Since 1M HCl has pH around 1, it is highly acidic. Blue litmus turns red in acidic solution and red litmus turns blue in basic solution. Using these principles, the correct option (C) correctly identifies the pH values and nature (acidic or basic) of the four given solutions in the table.
A metal 'X' is used in thermite process. When X is burnt in air it gives an amphoteric oxide 'Y'. 'X' and 'Y' are respectively:
Select washing soda from the following:
Consider the structures of the three cyclic carbon compounds A, B and C given below and select the correct option from the following :
The correct option is: 'A and C are isomers of hexane and B is benzene.' This is because cyclohexane (A) and compound C both have the molecular formula C6H12 and are cyclic saturated hydrocarbons (cycloalkanes). They are structural isomers of hexane (C6H14) but in cyclic form, meaning they have the same molecular formula but different structures. Benzene (B), with molecular formula C6H6, is an aromatic compound that is unsaturated due to the alternating double bonds. Therefore, A and C are cyclic isomers related to hexane derivatives, and B is benzene.
An organism which breaks down the food material outside the body and then absorbs it is
Consider the following statements about small intestine and select the one which is NOT correct:
The statement that correctly describes the characteristic(s) of a gene is:
Select from the following the correct statement about tropic movement in plants:
Select the INCORRECT match (between the plant and its vegetative part) from the following:
If four identical resistors, of resistance 8 Ω, are first connected in series so as to give an effective resistance Rₛ, and then connected in parallel so as to give an effective resistance Rₚ, then the ratio Rₛ⁄Rₚ is
In domestic electric circuits the wiring with 15 A current rating is for the electric devices which have
In the following diagram, the position of the needle is shown on the scale of a voltmeter. The least count of the voltmeter and the reading shown by it respectively are:
The least count of a voltmeter is the smallest division value on its scale. By observing the scale divisions in the diagram, the least count is 0.05 V. The needle points to a value between 1.75 V and 1.8 V, precisely at 1.8 V. Therefore, the correct option is '0.05 V and 1.8 V'. This means the instrument can read voltages in increments of 0.05 V, and the current reading shown is 1.8 V. Voltmeter readings measure the potential difference between two points and the needle position indicates the measured voltage.
The resultant magnetic field at point 'P' situated midway between two parallel wires (placed horizontally) each carrying a steady current I is
The correct answer is 'zero'. According to the right-hand rule, the magnetic field produced by each wire at the midpoint 'P' between them will be equal in magnitude but opposite in direction (one wire produces a field directed upward while the other produces a field directed downward at point 'P'). Since the two wires carry currents in the same direction and are placed parallel horizontally, their magnetic fields at the midpoint cancel each other out, resulting in a net magnetic field of zero at point 'P'.
Assertion (A): The colour of aqueous solution of copper sulphate turns colourless when a piece of lead is added to it.
Reason (R): Lead is more reactive than copper, and hence displaces copper from its salt solution.
Both A and R are true and R is the correct explanation of A. When lead is added to copper sulfate solution, the lead being more reactive than copper, displaces copper from the solution forming lead sulfate, which is colorless. This causes the blue color of the copper sulfate solution (due to Cu2+ ions) to fade and become colorless.
Assertion (A): Genes inherited from the parents decide the sex of a child.
Reason (R): X chromosome in a male child is inherited from his father.
Both statements A and R are true, but R is not the correct explanation of A. The sex of a child is determined by the chromosomes inherited from the parents. While it is true that the genes inherited from the parents influence the child's sex, the sex depends specifically on whether the sperm from the father carries an X or a Y chromosome. The X chromosome in a male child is actually inherited from the mother, not the father. The father contributes either an X chromosome (leading to a female child) or a Y chromosome (leading to a male child). Therefore, the reason given is incorrect.
Assertion (A): Blood clotting prevents excessive loss of blood.
Reason (R): Blood clotting is due to blood plasma and white blood cells present in the blood.
Assertion (A): The strength of the magnetic field produced at the centre of a current-carrying circular coil increases on increasing the number of turns in it.
Reason (R): The current in each circular turn has the same direction and the magnetic field due to each turn adds up.
Section C
(i) A compound 'X' which is prepared from gypsum has the property of hardening when mixed with proper quantity of water.
Identify 'X' and write its chemical formula.
(ii) State the difference in chemical composition between baking soda and baking powder.
(ii) Baking soda is sodium hydrogencarbonate with the formula NaHCO3. Baking powder is a mixture of baking soda (NaHCO3) and a mild edible acid like tartaric acid. Baking powder releases CO2 gas on heating or mixing with water, helping dough rise.
Write balanced chemical equation for the reaction that occurs when:
(i) blue coloured copper sulphate crystals are heated and
(ii) Sodium hydrogen carbonate is heated during cooking.
Copper sulphate pentahydrate (CuSO4 . 5H2O) →ᴴᴱᴬᵀ Anhydrous copper sulphate (CuSO4) + 5H2O (water vapour)
Balanced equation:
CuSO4 . 5H2O → CuSO4 + 5H2O
(ii) When sodium hydrogen carbonate (NaHCO3) is heated during cooking, it decomposes to form sodium carbonate (Na2CO3), water (H2O) and carbon dioxide (CO2).
Balanced equation:
2NaHCO3 →ᴴᴱᴬᵀ Na2CO3 + H2O + CO2
This reaction is used in cooking to make cakes rise as the carbon dioxide gas produced helps in leavening.
(a) Write the role of insulin in regulating blood sugar levels in human body. Mention the disease caused due to it.
(b) How is the timing and the amount of release of insulin in the blood regulated?
(a) Insulin is a hormone produced by the pancreas that helps regulate blood sugar levels in the human body. It allows cells to absorb glucose from the blood to use as energy or store for later use, thereby lowering the sugar level in the blood. If insulin is not secreted properly, blood sugar levels rise, leading to a disease called diabetes.
(b) The timing and amount of insulin released into the blood are controlled by a feedback mechanism. When blood sugar levels rise, pancreas cells detect this increase and produce more insulin. As blood sugar levels fall, insulin secretion decreases. This ensures that the blood sugar level is maintained within a normal range.
Name the type of blood (oxygenated / deoxygenated) transported by each of the following mentioning the path (i.e. from one organ (which place) to another (which place)).
(i) Vena cava
(ii) Pulmonary artery
With the help of a schematic flow chart, show the breakdown of glucose in a cell to provide energy -
(i) in the presence of oxygen
(ii) in lack of oxygen
(i) Breakdown of glucose in the presence of oxygen (Aerobic respiration):
Glucose enters the cell and undergoes glycolysis in the cytoplasm, where it breaks down into two molecules of pyruvate. The pyruvate then enters the mitochondria, where in the presence of oxygen, it is further broken down to produce carbon dioxide, water, and a large amount of energy (ATP).
(ii) Breakdown of glucose in the lack of oxygen (Anaerobic respiration):
When oxygen is not available, glucose is still broken down by glycolysis into pyruvate in the cytoplasm. However, instead of entering mitochondria, pyruvate is converted into lactic acid (in muscles) or alcohol and carbon dioxide (in some microorganisms), releasing less energy compared to aerobic respiration.
Name the part of the human excretory system where nephrons are found.
Write the structure and function of nephrons.
A narrow beam XY of white light is passing through a glass prism ABC as shown in the diagram:
Trace it on your answer sheet and show the path of the emergent beam as observed on the screen PQ.
Name the phenomenon observed and state its cause.
It is observed that the power of an eye to see nearby objects as well as far off objects diminishes with age.
(i) Give reason for the above statement.
(ii) Name the defect that is likely to arise in the eyes in such a condition.
(iii) Draw a labelled ray diagram to show the type of corrective lens used for restoring the vision of such an eye.
(i) The power of the eye to see nearby and far off objects diminishes with age because the ciliary muscles weaken and the eye lens loses its flexibility. This reduces the eye's ability to adjust its focal length for clear vision at various distances, a process known as accommodation.
(ii) This condition is called presbyopia.
(iii) To correct presbyopia, convex lenses (converging lenses) are used. They assist the eye lens by converging light rays before they enter the eye, helping to focus the image on the retina clearly.
How do harmful chemicals get accumulated progressively at each trophic level in a food chain?
Section D
(a) Identify the reducing agent in the following reactions:
(i) 4NH₃ + 5O₂ → 4NO + 6H₂O
(ii) H₂O + F₂ → HF + HOF
(iii) Fe₂O₃ + 3CO → 2Fe + 3CO₂
(iv) 2H₂ + O₂ → 2H₂O
(b) Define a redox reaction in terms of gain or loss of oxygen.
(i) NH3 as it loses hydrogen and is oxidised to NO.
(ii) H2O as it loses oxygen and is oxidised when reacting with F2.
(iii) CO as it loses oxygen and is oxidised to CO2.
(iv) H2 as it loses electrons and is oxidised to H2O.
(b) A redox reaction is a chemical reaction in which oxidation and reduction occur simultaneously. In terms of oxygen, oxidation is the gain of oxygen by a substance, while reduction is the loss of oxygen by a substance.
(a) Suggest one remedial measure each to counteract the change in pH in human beings in following cases :
(i) Production of too much acid in stomach during indigestion
(ii) Stung by a honey bee / nettle leaves
(b) Fresh milk has a pH of 6. When it changes into curd will its pH increase or decrease ? Why?
(a)(ii) When stung by a honey bee or nettle leaves, the affected area becomes acidic. To neutralize this acidity and reduce pain and swelling, one can apply a mild base such as baking soda solution or toothpaste.
(b) Fresh milk has a pH of around 6, which is slightly acidic. When milk turns into curd, its pH decreases and becomes more acidic due to the formation of lactic acid by bacteria during fermentation. Hence, the pH of curd is lower than that of fresh milk.
(i) State the role of ATP in cellular respiration.
(ii) What ensures sufficient exchange of gases in plants?
(iii) State the conditions on which the direction of diffusion of gases in plant depend upon.
(i) Role of ATP in cellular respiration:
ATP (Adenosine Triphosphate) acts as the energy currency of the cell. During cellular respiration, energy is released by breaking down glucose in the presence of oxygen. This energy is captured and stored in the form of ATP molecules. ATP then provides energy required for various cellular activities, including metabolic reactions, growth, and repair.
(ii) What ensures sufficient exchange of gases in plants?
Sufficient gas exchange in plants is ensured by tiny pores called stomata present mainly on leaves. Additionally, large intercellular spaces inside the leaf provide contact of all cells with air. Gases such as oxygen and carbon dioxide diffuse through the stomata, allowing plants to exchange gases effectively for photosynthesis and respiration.
(iii) Conditions affecting the direction of diffusion of gases in plants:
The direction of gas diffusion depends on environmental conditions and the plant's requirements. For example, during photosynthesis, plants take in carbon dioxide and release oxygen, so carbon dioxide diffuses inside while oxygen diffuses out. During respiration, oxygen is consumed and carbon dioxide is released, influencing the diffusion direction accordingly.
(a) Complete the following ray diagram to show the formation of image
(b) Mention the nature, position and size of the image formed in this case.
(c) State the sign of the image distance in this case using the Cartesian sign convention.
(b) The image formed in this case is virtual because the reflected rays do not actually meet but appear to diverge from a common point behind the mirror. The virtual image is erect (upright), larger than the object, and located behind the mirror (between the mirror and the focal point).
(c) According to the Cartesian sign convention, the image distance (v) is taken negative if the image forms on the same side as the object, which for a virtual image formed by a concave mirror is behind the mirror. Therefore, the image distance is negative in this case.
Give reasons for the following :
(a) Danger signals installed at airports and at the top of tall buildings are of red colour.
(b) The sky appears dark to the passengers flying at very high altitudes.
(c) The path of a beam of light passing through a colloidal solution is visible.
(a) Danger signals at airports and tall buildings are red because red light is least scattered by fog, smoke, or dust. This makes the red signal visible from a long distance and attracts immediate attention, which is crucial for safety.
(b) The sky appears dark to passengers flying at very high altitudes because the atmosphere is very thin there. At such heights, there is not enough air to scatter sunlight, so the sky looks dark instead of blue.
(c) The path of a beam of light is visible when passing through a colloidal solution due to the Tyndall effect. Tiny particles in the colloid scatter the light, making the beam’s path visible to our eyes, unlike in pure solutions.
(i) State the rule used to find the force acting on a current carrying conductor placed in a magnetic field.
(ii) Given below are three diagrams showing entry of an electron in a magnetic field. Identify the case in which the force will be (1) maximum and (2) minimum respectively. Give reason for your answer.
(i) The rule used to find the force acting on a current carrying conductor in a magnetic field is Fleming's Left-Hand Rule. According to this rule, if you stretch the thumb, the forefinger, and the middle finger of your left hand such that they are mutually perpendicular to each other, then:
- The First finger points in the direction of the Magnetic Field (from North to South).
- The seCond finger points in the direction of the Current (from positive to negative).
- The thuMb shows the direction of the Motion or the force acting on the conductor.
(ii) To identify the cases where force acting on the electron is maximum or minimum, we consider the direction of velocity of the electron relative to the magnetic field.
- The force on a charged particle moving in a magnetic field is given by the Lorentz force, which depends on the sine of the angle between velocity of the particle and magnetic field.
- When the velocity is perpendicular to the magnetic field (angle 90°), sin(90°) = 1, so the force is maximum.
- When the velocity is parallel or antiparallel to the magnetic field (angle 0° or 180°), sin(0°) = sin(180°) = 0, so the force is minimum (zero).
Therefore, among the three diagrams, the case where the electron enters the magnetic field perpendicularly experiences the maximum force, and the case where the electron enters parallel to the magnetic field experiences the minimum force.
(i) Draw the pattern of magnetic field lines of
(1) a current carrying solenoid
(2) a bar magnet
(ii) List two distinguishing features between the two fields.
(i) The magnetic field lines of a current-carrying solenoid are similar to those of a bar magnet. Inside the solenoid, the magnetic field lines are nearly parallel, close together, indicating a strong and uniform magnetic field. Outside the solenoid, the lines spread out and loop from one end of the solenoid to the other, forming closed loops. The direction of the magnetic field inside the solenoid is from the south pole to the north pole (as formed by the current direction).
The magnetic field lines of a bar magnet emerge from the north pole and curve around to enter the south pole, forming closed loops outside the magnet. Inside the bar magnet, the field lines run from the south pole back to the north pole. The pattern looks similar with field lines forming continuous loops in both cases.
(ii) Two distinguishing features between the magnetic field of a solenoid and a bar magnet are:
1. The magnetic field inside a solenoid is strong and uniform, whereas inside a bar magnet it may not be perfectly uniform.
2. The polarity of the solenoid’s magnetic field can be changed by reversing the direction of the current, but the poles of a bar magnet are fixed and cannot be reversed easily.
(i) Why does a kitchen garden called an artificial ecosystem while a forest is considered to be a natural ecosystem?
(ii) While designing an artificial ecosystem at home, write any two things to be kept in mind to convert it into a self-sustaining system. Give reason to justify your answer.
(i) A kitchen garden is called an artificial ecosystem because it is made and maintained by humans. People plant and care for the plants, control the growth of other organisms, and manage the ecosystem manually. In contrast, a forest is a natural ecosystem as it develops and sustains itself without human intervention. Forests contain various plants, animals, and microorganisms interacting naturally, maintaining a balanced environment.
(ii) While designing an artificial ecosystem at home, two important things to keep in mind are maintaining a balance between producers and consumers, and ensuring proper recycling of nutrients. Producers like plants create food through photosynthesis which supports consumers such as insects or small animals. Also, decomposers must be present to break down dead matter, recycling nutrients back into the soil. This balance helps the ecosystem to sustain itself by providing energy and nutrients continuously.
(i) Construct a food chain of four trophic levels comprising the following:
Hawk, snake, plants, rat.
(ii) 20,000 J of energy was transferred by the producers to the organism of second trophic level. Calculate the amount of energy that will be transferred by organisms of the third trophic level to the organisms of the fourth trophic level.
Plants → Rat → Snake → Hawk
Here, plants are producers and form the first trophic level. Rats, which eat plants, represent the second trophic level (primary consumers). Snakes, which eat rats, form the third trophic level (secondary consumers). Hawks, which feed on snakes, are the fourth trophic level (tertiary consumers).
(ii) Energy Transfer Calculation:
The energy transferred from producers (plants) to the second trophic level (rat) is given as 20,000 joules. According to the 10% energy transfer rule, only 10% of the energy is passed to the next trophic level at each step.
Energy transferred from the second trophic level (rat) to the third trophic level (snake) = 10% of 20,000 J = 2,000 J.
Energy transferred from the third trophic level (snake) to the fourth trophic level (hawk) = 10% of 2,000 J = 200 J.
Therefore, 200 joules of energy will be transferred from the third trophic level to the fourth trophic level.
(i) State the role of ATP in cellular respiration.
(ii) What ensures sufficient exchange of gases in plants?
(iii) State the conditions on which the direction of diffusion of gases in plant depend upon.
(ii) Sufficient exchange of gases in plants is ensured by stomata, which are tiny pores on the surface of leaves. Large intercellular spaces in the leaf allow gases like oxygen and carbon dioxide to diffuse efficiently to all cells.
(iii) The direction of diffusion of gases in plants depends on the concentration gradient of gases between the inside of the leaf and the surrounding air, as well as the requirements of the plant. Gases move from higher to lower concentration areas by diffusion.
Section E
A saturated organic compound A belongs to the homologous series of alcohols.
On heating A with concentrated sulphuric acid at 443K, it forms an unsaturated compound B with molecular mass 28 u.
The compound B on addition of one mole of hydrogen in the presence of nickel changes to a saturated hydrocarbon C.
(i) Identify A, B and C.
(ii) Write the chemical equations showing the conversion of A into B.
(iii) What happens when compound C undergoes combustion?
(iv) State one industrial application of hydrogenation reaction.
(v) Name the products formed when compound A reacts with sodium.
Compound A is ethanol (C2H5OH), a saturated alcohol.
Compound B is ethene (C2H4), an unsaturated hydrocarbon with molecular mass 28 u formed by dehydration of ethanol.
Compound C is ethane (C2H6), a saturated hydrocarbon formed by hydrogenation of ethene.
(ii) Chemical equation for conversion of A into B:
C2H5OH (ethanol) --(conc. H2SO4, 443 K)--> C2H4 (ethene) + H2O
Explanation: Ethanol on heating with concentrated sulphuric acid undergoes dehydration to form ethene and water.
(iii) Combustion of compound C:
C2H6 + 3.5 O2 --> 2 CO2 + 3 H2O + energy
Explanation: Ethane burns in excess oxygen to produce carbon dioxide, water and release energy.
(iv) Industrial application of hydrogenation reaction:
Hydrogenation is used in the food industry to convert vegetable oils (unsaturated fats) into margarine and other solid fats.
(v) Products formed when A reacts with sodium:
2 C2H5OH + 2 Na --> 2 C2H5ONa + H2
Explanation: Ethanol reacts with sodium to form sodium ethoxide and hydrogen gas.
(i) With the help of diagram, show the formation of micelles when soap is applied on oily dirt.
(ii) Take two test tubes X and Y with 10 mL of hard water each. In test tube X add a few drops of soap solution and in test tube Y add a few drops of detergent solution. Shake both for the same period.
(1) In which test tube will the formation of foam be more? Why?
(2) In which test tube is a curdy solid formed? Why?
(i) Formation of Micelles:
Soap molecules consist of two parts: a hydrophobic tail which is water-repellent and a hydrophilic head which is water-attracting. When soap is applied on oily dirt, the hydrophobic tails of soap molecules attach themselves to the oil/dirt particles, while the hydrophilic heads remain in the water. This arrangement forms tiny spherical structures called micelles, where the oily dirt is trapped inside the micelle. This allows the dirt to be emulsified and washed away with water, thus effectively cleaning the dirt.
[Diagram Description: Micelles showing soap molecules with tails attached to oily dirt inside and heads facing outward towards water]
(ii) Testing Soap and Detergent in Hard Water:
(1) Formation of Foam:
Foam formation will be more in test tube Y, which contains detergent solution. This is because detergents do not react with the calcium and magnesium salts present in hard water and thus produce good foam. On the other hand, soap reacts with these salts forming an insoluble substance that reduces foam formation.
(2) Formation of Curdy Solid:
Test tube X, containing soap solution, will form a curdy white solid called 'scum.' This happens because soap reacts with calcium and magnesium ions present in hard water, forming insoluble calcium or magnesium salts. These precipitates appear as a sticky curdy solid, which decreases the cleaning efficiency of soap in hard water.
(a) Name the parts of a bisexual flower that are not directly involved in reproduction.
(b) Differentiate between self pollination and cross pollination. List any two significance of pollination.
(c) What is the fate of ovules and ovary after fertilization in a flower?
(a) The parts of a bisexual flower that are not directly involved in reproduction are the sepals and petals. Sepals protect the flower before it blooms, while petals attract pollinators such as bees and butterflies.
(b) Self-pollination occurs when pollen from the anther of a flower falls on the stigma of the same flower. This means the flower fertilizes itself with its own pollen. In contrast, cross-pollination happens when pollen is transferred from the anther of one flower to the stigma of a different flower, usually from another plant of the same species. Cross-pollination helps increase genetic diversity in plants.
Two significances of pollination are: (1) It helps in the process of fertilization by bringing male gametes to the female part of the flower, ensuring seed formation. (2) It aids in the production of fruits and seeds, which are crucial for the reproduction and survival of plant species.
(c) After fertilization, the ovules inside the ovary develop into seeds, which contain the embryonic plant. The ovary itself matures and changes into a fruit that protects the seeds and helps in their dispersal.
(a) An electric iron consumes energy at a rate of 880 W when heating is at the maximum rate and 330 W when the heating is at the minimum. If the source voltage is 220 V, calculate the current and resistance in each case.
(b) What is heating effect of electric current ?
(c) Find an expression for the amount of heat produced when a current passes through a resistor for some time.
Given power P and voltage V, the current I can be calculated using the formula I = P / V. For the maximum heating:
Power P = 880 W, Voltage V = 220 V
Current I = 880 / 220 = 4 A
Resistance R = V / I = 220 / 4 = 55 ohms
For the minimum heating:
Power P = 330 W, Voltage V = 220 V
Current I = 330 / 220 = 1.5 A
Resistance R = 220 / 1.5 ≈ 146.67 ohms
(b)
The heating effect of electric current refers to the phenomenon where an electric current passing through a conductor produces heat. This happens because the moving electrons collide with the atoms of the conductor, causing them to vibrate and generate heat energy. This effect is the basis for many electrical appliances like electric irons, heaters, and toasters, which convert electrical energy into heat energy.
(c)
The amount of heat produced (H) when a current (I) passes through a resistor (R) for some time (t) is given by the formula:
H = I² × R × t
This equation shows that the heat produced is directly proportional to the square of the current, the resistance, and the time for which the current flows through the resistor.
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