Ques 1: AB is current-carrying conductor in the plane of the paper as shown in figure. What are the directions of magnetic fields produced by it at the points P and O? If r1 > r2, where will the strength of the magnetic field be larger?
Ans: Applying right-hand thumb rule, the direction of magnetic field produced by a current-carrying conductor at Point P into the plane of paper Point Q out of the plane of paper. As magnetic field is inversely proportional to distance, the field at Q will be larger than the field at p(r1 > r2).
Ques 2: Identify the compound X on the basis of the reactions given below. Also, write the name and chemical formulae of A, B and C.
Ans: The compound X is NaOH (sodium hydroxide). Chemical formulae of A, B and C are A → Na2ZnO2 (Sodium zincate) B → NaCl (Sodium chloride) C → CH3COONA (Sodium acetate)
Ques 3: With labelled diagrams describe an activity to find out the conditions under which iron rusts.
Ans: Activity to show that air and water are necessary for rusting.
Case I
In an absolutely clean and dry test tube [Fig. (a)] place about 2 g of anhydrous calcium chloride and then a shining nail. Put stopper on the mouth test tube and place it aside for a week. The anhydrous calcium chloride is used to absorb moisture from the enclosed air. It is seen that the nail does not rust. Thus, we can conclude that dry air does not cause rusting.
Case II
Fill 3/4 of another test cube with water [Fig. (b)], which is already boiled, so that it does not contain any dissolved air. Over the water, pour 1 cc of any oil so as to cut off the atmospheric air. In the water, place a shining nail and put stopper on the mouth of test tube. After a week, it is seen that the nail does not rust. Thus, we conclude that pure water does not cause rusting.
Case III
Place a shining nail in a third test tube [Fig. (c)] and half fill it with tap water. Put stopper on the mouth of test rube. After a week, it is seen that the nail rusts. Thus, we can conclude that air and water (moist air) is necessary for rusting.
Ques 4: (a) How is the direction of electric current related to the direction of flow of electrons in a wire?
(b) Calculate the current in a circuit if 500 C of charge passes through it in 10 minutes.
Ans: (a) The conventional direction of electric current is opposite to the direction of flow of electrons in a wire.
(b) Q = 500 C t = 10 min = 10 x 60 = 600 s
Ques 5: How electric potential is generated in a conductor during the flowing charges?
Ans: When an electric charge moves through a conductor an electric field is set up by the conductor the electric field interacts with moving charges and hence some energy is spent in moving the charges in forward direction. This energy spent is the cause of generation of electric potential.
Ques 6: How will the magnetic field produced at a point due to a current-carrying circular coil change if we
(a) increase the current flowing through the coil?
(b) reverse the direction of current through the coil?
(c) increase the number of turns in the coil?
Ans: Magnetic field (B) at the centre of the circular coil (a) increases if the current is increased as. (b) reverses on reversing the current. (c) increases if the number of turns in the coil increases as field is directly proportional to the number of turns.
Ques 7: Identify the reducing agent in the following reactions
(a)
(b)
(c)
Ans: (a) Ammonia (NH3) is the reducing agent.
(b) Fluorine (F2) is the reducing agent.
(c) Carbon monoxide (CO) is the reducing agent.
Ques 8: Two lamps, one rated 60 W at 220 V and the other 40 W at 220 V, are connected in parallel to the electric supply at 220 V
(a) Draw a circuit diagram to show the connections.
(b) Calculate the current drawn from the electric supply.
(c) Calculate the total energy consumed by the two lamps together when they operate for one hour.
Ans: (a) The circuit diagram to show the given connection is shown below
(b) Current drawn by 40 W lamp
Current drawn by 60 W lamp,
∴ Total electric current drawn from the electric supply
(c) Total energy consumed in one hour = 60 x 1 + 40 x 1 = 100 Wh = 0.1 kWh
Ques 9: A gas is produced in the laboratory is highly soluble in water. Its colourless solution turns pink when a few drops of phenolphthalein is added to it. What is the nature of this gas?
Ans: The nature of the gas is basic because it turns phenolphthalein pink. The reaction takes place in aqueous solution.
Ques 10: Which is the internal energy reserve in plants? Do the animals have the same energy reserve?
Ans: The carbohydrates which are not used immediately are stored in the form of starch, which serves as the internal energy reserve. In animals, glycogen serves as energy reserve.
Ques 11: Name two hormones secreted by pancreas. Write one function of each hormone.
Ans: The two hormones secreted by pancreas and its function are
(i) Insulin Recognition of glucose by cells for absorption and conversion of glucose into glycogen in liver and muscles.
(ii) Glucagon Formation of glucose from glycogen and other sources and its release into blood.
Ques 12: Identify the parts labelled X, Y and Z in the given circuit.
Ans: X = Milliammeter Y = Resistor Z = Voltmeter
Ques 13: How is the supply of electricity maintained by a windmill when there is no wind and by a solar panel when there is no sun?
Ans: In both the cases, the generated electricity is stored in a storage cell like battery. It provides the energy needs during a period when there is no wind in the case of windmill and no sun in the case of a solar panel.
Ques 14: Four identical cells of emf 1.5 V each were connected. The potential difference between the two points A and B would be equal to 6.0 V. Draw the circuit.
Ans: The required circuit is given below
Ques 15: Plant respiration is slower than animal respiration. Suggest one reason for it.
Ans: Plants do not need as much of energy as the animals since they are neither mobile nor active. Hence, their respiration is slower.
Ques 16: The best photosynthetic lights are red and blue. Why?
Ans: Red and blue are best photosynthetic lights because they stimulate the chloroplasts maximum.
Ques 17: A voltmeter has a least count of 0.05 V While doing Ohm's law experiment, a student observed that the pointer of the voltmeter coincides with 15th division. Find the correct reading.
Ans: Correct reading = Least count X Number of divisions = 0.05 x 15 = 0.75 V
Ques 18: When do guard cells swell?
Ans: Guard cells swell when water flows into them causing the stomatal pore to open.
Ques 19: Suggest two salts that are used in black and white photography.
Ans: Silver chloride and silver bromide are used in black and white photography.
Ques 20: Identify the procedure used in the working of an artificial kidney.
Ans: The procedure used for the working of an artificial kidney is dialysis.
Ques 21: On putting a few drops of a liquid on a pH strip, the colour of the pH strip changed to red. Identify the compound.
Ans: The compound is hydrochloric acid i.e., HCl that turns pH paper red.
Ques 22: What happens chemically when quick lime is added to water?
Ans: Quick lime or calcium oxide reacts vigorously with water to form laked lime or calcium hydroxide redesign large amount of energy.
Ques 23: Would you consider hydrogen to be a cleaner and more efficient fuel than CNG?
Ans: Yes, CNG is a cleaner fuel because on burning, hydrogen produces only water vapour which is non-polluting.
Ques 24: Name the products formed in each of the following cases
(a) Hydrochloric acid reacts with caustic soda.
(b) Granulated zinc reacts with caustic soda.
(c) Carbon dioxide is passed into lime water.
Ans: (a) Sodium chloride and water
(b) Zinc hydroxide and hydrogen
(c) Calcium carbonate and water
Ques 25: (a) What happens at the synapse between two neurons? (b) What is the function of receptors in our body?
Ans: (a) At the synapse, the two neurons join together and transfer message from one neuron to other.
(b) Receptors are the special cells present in our sense organs. They detect all the information from our environment and feed it to the nervous system. For example, gustatory receptors present in our tongue detect taste of our food whereas olfactory present in our nose detect smell.
Ques 26: Mention the functions of (a) Thyroxine (b) Calcitonin and (c) Testosterone.
Ans: (a) Thyroxine It regulates the metabolism of carbohydrates, fats and proteins in the body so as to provide the best balance for growth.
(b) Calcitonin It regulates the calcium and phosphate levels in the blood.
(c) Testosterone It regulates the male accessory sex organs and secondary sexual characters like moustache, beard and voice.
Ques 27: Laxmi and her mother went to the market to purchase some household articles. Laxmi's mother was going to purchase 100 W electric bulb. Laxmi advised her to purchase CFL. She told her mother that it will consume less amount of power and will save electricity.
(a) What qualities do you notice in Laxmi?
(b) A 100 W bulb and a 500 W bulb are joined in parallel to the mains. Which bulb will draw more current?
Ans: (a) Laxmi is aware, has presence of mind, concern for family and capable to apply knowledge.
(b) Power (P) = Potential difference (V) x Current ∴ I2 > I1 Thus, 500 W bulb will draw more current.
Ques 28: Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes? Or How does a solenoid behave like a magnet? Can you determine the North and South poles of a current-carrying solenoid with the help of a bar magnet. Explain.
Ans: Principle of an electric generator It works on the phenomenon of electromagnetic induction i.e., when a coil is rotated in a uniform magnetic field, an electric current is induced in a closed circuit of the coil. Working of an AC generator when the armature coil ABCD rotates in clockwise direction in the magnetic field, the magnetic flux linked with it changes. Hence, the induced current flows in the direction in ABCD as per Fleming's right-hand rule. Thus, the current in the external circuit flows from B2 to B1.
After half rotation, arm AB starts moving down while CD starts moving up. Hence, the direction of current in the coil reverse. Net induced current flows in the direction DCBA. Hence, the current in the external circuit flows from B2 to B1. Therefore, the polarity of induced current between the brushes 5, and B changes after every half rotation. Such current is called alternating current. Function of brushes The two carbon brushes provide the path to the induced current to flow from the armature and the slip rings to the external circuit containing load resistance.
Or
A solenoid is a long coil of circular loops of insulated copper wire. Magnetic field lines are produced around the solenoid when a current is allowed to flow through it. The magnetic field produced by it is similar to the magnetic field of a bar magnet. The field lines produced in a current-carrying solenoid is shown in the following figure
In the given figure, when the North-pole of a bar magnet is brought near the end connected to the negative terminal of the battery, the solenoid repels the bar magnet. Since like poles repel each other, the end connected to the negative terminal of the battery behaves as the North pole of the solenoid and the other end behaves as a South pole. Hence, one end of the solenoid behaves as a North pole and the other end behaves as a South pole.
Ques 29: Sketch a schematic flow chart showing the breakdown of glucose in a cell to provide energy in the following conditions
(a) In the presence of oxygen.
(b) In the absence of oxygen.
(c) Where there is a lack of oxygen.
Or
(a) Draw a diagram to show the nutrition in Amoeba and label the parts used for this purpose. Mention any other purpose served by this part other than nutrition.
(b) Name the glands associated with digestion of starch in human digestive tract and mention their role.
(c) How is required pH maintained in the stomach and small intestine?
Ans:
Pseudopodia serves the purpose of locomotion apart from nutrition.
(b) The salivary gland is associated with digestion of starch in human digestive tract. It secretes saliva with the help of enzyme salivary amylase which converts starch into maltose (sugar).
(c) Gastric glands present on the walls of the stomach release HCl acid. It creates an acidic medium, which facilitates the action of enzyme pepsin. Bile juice form liver makes the food alkaline in small intestine for the pancreatic enzymes to act.
Ques 30: What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption? Or What is solar water heater? With the help of a schematic diagram, describe the principle and working of a solar water heater.
Ans: The demand of energy is increased due to the industrialisation all over the world. The environmental consequences of increasing demand for energy are as follows
(i) Use of fossil fuels is increasing air pollution which is not good for our health.
(ii) Air pollution is causing much damage to the ecosystem.
(iii) Greenhouse effect has resulted in global warming which is manifesting itself in strange changes in the weather pattern around the world.
(iv) Too much exploitation of fossil fuels is going to create a situation when there would be not fossil fuel.
(2) The steps to reduce energy consumption
(i) Judicious use of energy is the only way.
(ii) Use public transport instead of private modes of transport.
(iii) Use bicycle whenever possible.
(iv) Walk for short distance commute.
(v) Avoid unnecessary use of modern gadgets which consume lot of energy.
(vi) Use appliances that run using non-conventional sources like solar cooker etc.
Or
Solar Water Heater It is a device which heats the water using solar energy.
Principle
(i) A black surface absorbs more heat as compared to white or reflecting surface under identical conditions.
(ii) Greenhouse effect is provided by glass lid.
Structure It consists of an insulated box which is painted black from inside having a coiled black chrome painted copper pipe. The box is covered with glass lid so as to prevent heat loss by convection and radiation. The two ends of the copper pipe of solar water heater are joined to the water storage tank which is insulated to prevent heat loss.
Working
The copper pipe warms up due to solar radiations incident on it.
The glass lid on the box provides the greenhouse effect to optimise the heating.
The water flowing through the tube gets heated by absorbing solar energy.
The hot water becomes lighter which flows up into the tank and heavier cold water from same tank enters into the copper pipe.
The circulation of water from the tank through the pipe and back to the same tank continues automatically, due to density difference between cold and hot water.
∴ I2 > I1 Thus, 500 W bulb will draw more current. 
After half rotation, arm AB starts moving down while CD starts moving up. Hence, the direction of current in the coil reverse. Net induced current flows in the direction DCBA. Hence, the current in the external circuit flows from B2 to B1. Therefore, the polarity of induced current between the brushes 5, and B changes after every half rotation. Such current is called alternating current. Function of brushes The two carbon brushes provide the path to the induced current to flow from the armature and the slip rings to the external circuit containing load resistance.
