In case of a fire, before the firemen uses the water hoses, they shut off the main electrical supply for the area. A tester is used to check the conduction of electricity through two liquids, labelled A and B. Distilled water does not have any salts dissolved in it, but rain water may have some impurities in it. Question 13. If not, what can we do to make it conducting? Add a little sugar to the distilled water in the third cap and dissolve it. Answer: What are conductors ? Nickel and chromium-coated articles are used in automobiles and household appliances. the concentration of electricity; can be positive or negative. Question 9. Question 6. When electric current is passed in water hydrogen ions (H+) move towards cathode and get collected over it. Question 2. Repeat the activity with other liquids such as tap water, vegetable oil, milk, honey. However, if the bulb does not glow, it means that the tester is not working. What is electrolysis ? But when salt is dissolved in distilled water and again tested, the bulb glows which shows that water containing salts conduct electricity. Bring your tester over this cap and let the ends of the tester dip into lemon juice or vinegar as shown in Fig. The water used in the water hoses is not pure water and is a good conductor of electricity. This is static electricity. We will need copper sulphate and two copper plates of size around 10 cm x 4 cm. So, the compass needle showed deflection. 14.3). 14.2). Changes of colour of solutions may occur depending on what solution and electrodes are used. Electric current can produce magnetic effect also. 25% of the city of San Francisco's energy is generated by wind power. Collect a few small plastic or rubber caps of discarded bottles and clean them. This happens because the when current is passed, the K+ ions are attracted to the metal sheet. Answer: The decomposition of an electrolyte when electricity is passed through it, is called Which one of the following is a weak electrolyte ? Paheli had heard that rainwater is as good as distilled water. Question 1. Solution: The compass needle will show deflection with tap water, lemon juice and sodium chloride solution. Now repeat Activity 14.2 using this tester. You may also get distilled water from a medical store or a doctor or a nurse). Does distilled water conduct electricity? Now immerse the electrodes in this solution. To her surprise, she found that the compass needle showed deflection. Answer: When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Does pure water conduct electricity? Dissolve two teaspoonfuls of copper sulphate in it. (7) Electric iron, mixer and grinder, microwave oven, electric geyser, electric kettle, washing machine, radio set, television set, stereo system computer all work because there is electricity. Activity 1 (NCERT Textbook, Page 173) Recall the definition of a chemical change that you learnt in Class VII. Question 3. It cannot be said for sure that liquid does not conduct electricity because : Question 2. Take the tray from inside a discarded matchbox. It is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. If the electric potential is negative in the direction of electric current and the In this activity, if the bulb does not glow, it means that either the connections of the circuit are loose or the bulb is fused or cells are used up. Water is a solution of salts and so it is a good conductor of electricity. Answer: Answer: LEDs emitting white light can be used instead of bulbs. Solving the Chemical Effects of Electric Current Multiple Choice Questions of Class 8 Science Chapter 14 MCQ can be of extreme help as you will be aware of all the concepts. Question 10. Answer: Answer: Question 11. The bulb in the tester does not glow when current is passed through it. Take out the ends of the tester from the lemon juice, dip them in water and then wipe them dry. This process is known as chemical effects of current. Question 14. Electric charge on ions is used for writing with an electric pen. (c) half on the anode and half on the cathode (c) electrolysis Clean copper plates with sand paper. Activity 7 (NCERT Textbook, Page 177) During electroplating, the silver metal from the anode is deposited on the cathode. Air is an insulator of electricity. Prepare a list of objects around you that are electroplated. Can we call the change taking place in the solution a chemical change? Add a few drops of lemon juice or dilute hydrochloric acid to distilled water in one cap. It gets deposited on the Answer: Answer: You would conclude that How are bridges and automobiles prevented from rusting ? How would you classify lemon juice or vinegar—a good conductor or a poor conductor? Activity 3 (NCERT Textbook, Page 174) Note down the terminal of the battery with which this electrode is connected. The bulb may not glow because of the following reasons: Make sure that the metal caps of the carbon rods are outside the water. Electricity Uses. Conductors : lemon juice, tap water. Answer: Deposits can be seen in containers uses for storing water. Name one non-metal which a good conductor of electricity. The lightning conductor used in building protects the building by : This completes the circuit of the tester and the bulb should glow. Answer: Coal is generally used in thermal power generation which further helps to produce electricity. (c) cathode The sum of electric potential differences along any closed loop in a DC circuit is zero. Record your observations in Table 14.1. What is the difference between current flowing through metals and current flowing through liquids ? Thus food, stored in iron cans, is prevented from being spoilt due to iron by electroplating it by tin. Terms in this set (11) Electricity. Question 11. (i) liquid A is a better conductor than liquid B. Answer: Take care that the ends are not more than 1 cm apart but at the same time do not touch each other. Answer: Chemical Effects of Electric Current Class 8 Science NCERT Intext Activities Solved. the movement of electrons. Firemen shuts off the main electrical supply for the area because water is a good conductor of electricity and the firemen can get electrocuted. Answer: Question 6. Question 19. Question 7. Why is chromium used for electroplating ? Explain. (d) The process of depositing a layer of any desired metal on another material by means of electricity is called _______ In order to make electricity useful, we had to find a way to not only generate large amounts of electricity, but to somehow store it. dtoiakramer PLUS. Your tester with two free ends of the wire is ready. The loss of copper from solution is cqmpensated and the process goes on. Many powerplants around the globe produce this resource for the massive consumption now experienced but often at great cost to the environment. Question 3. Can you explain the reason ? Take a filter paper soaked in potassium iodide solution to which a pinch of starch is added. The articles to be plated should be cleaned throughly to remove dust, grease or any deposit on it. Pour one teaspoon of lemon juice or vinegar in one cap. Answer: During electrolysis of water, why does hydrogen collect on cathode and oxygen collect on anode ? Gradually, a layer of copper builds up on the plate. Solution: What can be the possible reasons for this ? These MCQ Questions on Chemical Effects of Electric Current Class 8 with answers pave for a quick revision of the Chapter thereby helping you to enhance subject knowledge. Answer: . (b) electrical energy into chemical energy Leave the other end free. Take out carbon rods carefully from two discarded cells. 7. Wrap copper wires around the metal caps of the carbon rods and join them to a battery (Fig. Can you ex¬plain the reason? Clean their metal caps with sand paper. A household uses the following electric appliances: (i) Refrigerator of rating 400 W for ten hours each day. Attach the free ends of the wires to a LED. Why? Thus water which is free of salts are poor conductors while water with salts is a good conductor of electricity. Have you ever imagined how electricity is produced and what's the science behind it? We call these two rods electrodes. These Class 8 trucks stand out, not only for their appealing exteriors but for the latest computer technology, keeping them steps ahead of other manufacturers’ trucks. [NCERT] as a point source of light in laser beam torches. (b) coating Solution: What is CFL ? Tesla won and AC is delivered to most homes still today. How can the magnetic effect be used as a tester ? (a) Aluminium Which electrode should be attached to the positive terminal of the battery and why? Now in the second cap containing distilled water, add a few drops of a base such as caustic soda or potassium iodide. Solution: Answer: Humans cannot survive without it. may be the current is so weak that it does not heat the filament of the bulb allowing it to glow. Explain why they do this. The free copper, being positively charged, gets drawn to the negative terminal of the battery and gets deposited on it. We cannot make the whole article from it because it is a very costly metal. What do you find? Answer: Question 10. Question 8. The entire NCERT textbook questions have been solved by best teachers for you. Solution: (a) Most liquids that conduct electricity are solutions of ______ , ______ and ______ An electric eel is a fish that makes its own electricity ,Lightning is spark of electricity in the air and bulb uses electricity to glow. (b) Oxalic acid The 21 all-electric BYD heavy duty trucks used by Anheuser-Busch in California since 2019 is still the largest Class 8 truck deployment in North America. LED is Light Emitting Diode. Open up your curtains and let the sun shine in! But when salt is dissolved in pure water, it conducts electricity. Sun is the main source of heat energy. Add a teaspoonful of salt or a few drops of lemon juice to water to make it more conducting. Question 1. Question 4. What is the basic principle of electric pen ? 3.00. b) An electric iron of resistance 20Ωtakes a current of … You would conclude that. (b) The passage of an electric current through a solution causes _______ effects. The rainwater showed deflection with the tester because it is not as pure as distilled water. Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? If the ends of the wire of tester are touched for a long time, the cells will be finished very soon. Allow the current to pass for about 15 minutes. Question 18. Observe the electrodes carefully. After the electroplating of a spoon with silver, it was found that the anode has become thin. Why ? The electrical resistivity of few materials is given below in ohm-meter. Why should you not do the experiments on electricity by using electric supply from mains ? Do you find a deflection in the compass A metal is released in the electrolysis of a salt. In 2014, nearly half of electricity used by U.S. manufacturers was for operating machinery.3 1. Compass needle shows deflection due to magnetic effect of electric current. How should LED be connected ? The thick rod of impure copper plate is to be attached to the positive terminal of the battery because when electric current is passed through the copper sulphate solution, it gets dissociated into copper and sulphate. Electric eels use electricity to ward off enemies. Answer: As water is a good conductor of electricity so it can cause electrocution. Question 8. Dinesh can study the chemical effect of current at home very easily. Answer: The electrode, connected to the positive terminal of a battery, is called (6) Electricity is used to pump underground water from tube wells for irrigation in field. If it is still not working then replace the cells with fresh cells. Therefore, we can be electrocuted in case we touch appliances with wet hands. In case of a fire, before the firemen use the water hoses, they shut off the main electrical supply for the area. Question 14. The liquid is a conductor and the circuit is also complete, but the bulb does not glow. (b) chemical Answer: Calculate the electricity bill of the household for the month of June if the cost per unit of electric energy is Rs. Write on the paper with the end of the wire connected to the positive terminal. (Instead of carbon rods, you may take two iron nails about 6 cm long.) NCERT Solutions for Class 6, 7, 8, 9, 10, 11 and 12. Answer: Conducting properties of liquid cannot be compared in this manner. Do you find a coating over it? The bulb does not glow in the setup shown in Fig. Question 20. (Remember to wash and wipe the ends of tester after testing each liquid). Can you explain the reason ? Answer: (i) liquid A is a better conductor than liquid B. Wrap an electric wire a few times around the tray. Connect the negative terminal of battery to the metal sheet. Created by. Answer: Question 12. (c) Sodium A child staying in a coastal region tests the drinking water and also the seawater with his tester. Spell. Domestic Use; Generating Electricity. By volume of hydrogen gas is twice the volume of oxygen gas. If the current in the circuit is small, how can we test its presence ? Take another piece of wire and connect it to the other terminal of the battery (Fig. Copper from impure rod is sought to be transferred to the thin copper plate. However, if the bulb does not glow, it means that the tester is not working. Objects that are electroplated are door handles, taps, rims of cycles, showers, the handlebar of cycles and bikes, gas burner, tin cans, metallic almirahs, buckles of belts, etc. Two famous scientists, Thomas Edison and Nikola Tesla, once had an argument over what kind of electricity we should use in our homes, AC or DC. Thus, lemon juice, vinegar, tap water, milk, curd and water, and soda are good conductors of electricity while vegetable oil, honey, kerosene oil, and distilled water are poor conductors of electricity or insulators. This shows that distilled water does not conduct electricity. (d) Vinegar needle the moment you dip the free ends of the tester in lemon juice? (b) Alcohol Grade 8 Science - Electricity. So she collected some rainwater in a clean glass tumbler aifd tested it using a tester. A tester can be made by attaching one free end of the wire to a terminal of a battery and another wire from other terminal of the battery to a bulb. From the other plate, an equal amount of copper gets dissolved in the solution. Free PDF Download - Best collection of CBSE topper Notes, Important Questions, Sample papers and NCERT Solutions for CBSE Class 8 Science Chemical Effects of Electrical Current. If not, what can we do to make it conducting ? Explain the process of electroplating of copper. Test which solutions conduct electricity and which do not. Hence, water is avoided in extinguishing electric fires. Answer: (d) electroplating. Answer: Activity 6 (NCERT Textbook, Page 176) Top Is air an insulator or conductor of electricity ? No, it is not advisable for electrician to carry out electrical repairs during heavy downpour because water is a good conductor of electricity and the person can get shock. Answer: Electroplating. In each case observe whether the magnetic needle shows deflection or not. Answer: Use the tester to test whether distilled water conducts electricity or not. Rainwater is pure water which is an insulator but it gets mixed with air pollutants like sulphur dioxide and nitrogen oxides and form acidic solution, which is a good conductor of electricity. resistance 240 = 240 V R= 8 Current (I) = 30 =8A V R= I 39. Answer: This completes the circuit of the tester and the bulb should glow. Water is dissociated into its constituent gases, i.e., hydrogen and oxygen. Explain your answer. Apart from chemical effect, which other effect electric current produce ? Hydrogen and Oxygen. Answer: If the magnetic compass shows deflection glows, it is a conductor, but if it does not deflect, it is an insulator. Use plating artificial jewellery with gold. It is found that the bulb of the tester glows brightly for liquid A while it glows very dimly for liquid B. Solution: A tester is used to check the conduction of electricity through two liquids, labelled A and B. When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Name the gases formed when electric current is passed in water containing a few drops of acid ? The process of depositing a layer of any desired metal on another material by means of electricity is called …………. Answer: (d) photodiode Electricity is a form of energy produced by charges. (c) If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the ________ terminal of the battery. Instead the iron can be galvanised or painted. The free copper gets deposited on the plate acting as cathode. Answer: List the possible reasons. Why the iron cans are electroplated with tin ? Question 12. Question 7. Answer: PLAY. Dec 27, 2020 - Important Questions - Chemical Effects of Electric Current, Science, Class 8 | EduRev Notes is made by best teachers of Class 8. Can you explain the reason? What could be the reasons ? (a) Copper Topics and Sub Topics in Class 8 Science Chapter 14 Chemical Effects of Electric Current: Question 1. No, it is highly dangerous to carry out the electrical repairs outdoors during the heavy downpour. What colour is the coating? Answer: (c) Dilute sulphuric acid If the tester is put in distilled water, the bulb of the tester does not glow. The two free ends of wire are connected to the material to be tested. Examples are copper, aluminium, etc. Current electricity is when an electrical charge is given a path to move through. This steam is used to turn turbines at high speed in a strong magnetic field. Question 13. Dinesh is wants to study the chemical effect of current at home. A charge that remains stationary on an insulator. (b), Question 3. Answer: Distilled water is a If the ends of the wire of tester are touched for a long time, what will happen ? Graphite. Which of these materials can … RVers parked in areas where they do not need air conditioning will use much less electricity than RVers who do need it. (a) anode Give the construction of LED. Example 1• An electric rice cooker operates at 240 V and uses a current of 8 A. What is LED? Answer: Jaya sets up a circuit as given below. [NCERT] Fill in the blanks. The bulb does not glow even though the circuit is complete because the current is too small. Dip the ends of the wire in the given liquid. View and Download PowerPoint Presentations on Electricity And Magnetism Class 8 PPT. Place them in fresh lemon fruit. All the best! Method : Question 2. (b), Question 6. A child staying in a coastal region test the drinking water and also the seawater with his tester. What are insulators ? Good conductors are those conductors that allow current to pass through them. Question 9. Answer: Decoration of articles by giving them a layer for e.g., silver plating on cutlery. (c) negative [NCERT] The salts separate out and deposit on the sides of the container. How can you make a tester for testing whether a given material is a conductor or an insulator ? 14.4). These charges can be at rest or moving .Learn how these moving charges constitute current electricity. (ii) The bulb may be fused. Answer: Pour about two teaspoonfuls of distilled water in each of them. Therefore, it becomes thin. Answer: Which out of the following does not conduct electricity ? Compact Fluorescent Lamps. Answer: How can he do it ? If you pass current through copper sulphate solution, copper gets deposited on the plate connected to the ……….. terminal of the battery. Name three liquids, which when tested in the manner shown in figure, may cause the magnetic needle to deflect. Tin is less reactive than iron. (i) The wires in the circuit may be loosely connected. Solution: Zinc coatings prevent the corrosion of steel articles. Write. Electroplating is the process of depositing a thin film of one metal over another metal by passing electric current through an electrolyte. Which of the following metal is not extracted by electrolysis? Using natural light … (d) semi-insulator [NCERT] No, pure water doesn’t conduct electricity. A change in the electric potential change equals the change in electric potential energy per unit charge. Answer: Connect the copper plates to the terminals of a battery and immerse them in copper sulphate solution (Fig. Answer: 14.5. may cause the magnetic needle to deflect. Question 13. LEDs require very little energy and glow even if a small current is passing through the circuit. Answer: Question 21. The sea water contains more salts dissolved in it as compared to the tap water. Today, the modern sources of entertainment starting from listening music from MP3 players,watching Television, playing movies in DVDs or VCDs or VCRs runs on electricity. Why we cannot make the whole article with chromium ? A thin plate of pure copper and a thick rod of impure copper are used as electrodes. Question 5. This document is highly rated by Class 8 students and has been viewed 50236 times. Do you find any difference in any one of them? Add a few drops of dilute sulphuric acid to copper sulphate solution to make it more conducting. (b) insulator Does the bulb of the tester glow? Learn. Which is the most common application of chemical effect of current ? Activity 2 (NCERT Textbook, Page 773) (c) chemical energy into electrical energy Jake three clean plastic or rubber caps of bottles. Take two pieces of copper wire and iron wire. What are electrodes ? Do you notice any gas bubbles near the electrodes? We prefer not to do electroplating on iron used for bridges because it is very costly. If the tester is working, it can be used to test the materials, i.e., whether it is a conductor or non-conductor of electricity. What is electroplating? Why should you not touch electrical appliances with wet hands ? (You may obtain distilled water from your school science lab. Yes, the solution does conduct electricity. We can test the presence of the small current by using a LED instead of the bulb. But the bulb does not glow. Question 4. Check that all the connections are tight. (iii) The cells may be used up. Answer: Explain. (8) Electric trains runs with electricity. For example: All metals including metal wires, copper wires, aluminium foil, etc. 8. (b), Question 8. Lighting 1 Embrace natural light. Question 3. The process that you saw in Activity 14.7 is used for purification of copper. The free copper gets drawn to the plate connected to the negative terminal of the battery and gets deposited on that plate. Answer: In metals electric current is conducted by flow of electrons. Answer: Question 12. Fun facts about the Uses of Electricity. Does pure water conduct electricity ? The temperature around the electroplating equipment should be optimum. The major uses of electricity and their shares of total electricity use by the commercial sector in 2014 were 2. machine drives (motors)48.2% 3. process heating and boiler use14.4% 4. facility heating, ventilation, air conditioning, and cooling9.5% 5. electrochemical processes6.8% 6. process cooling and refrigeration7.3% 7. lighting6.5% 8. other miscellaneous processes and facility uses7.3% Understanding the power of electricity we humans harness is necessary for the wise use and creation of this valuable resource. Question 11. Is it possible that the connections are loose? We should not do the experiments on electricity by using electric supply from the mains because there is large amount of current and the person using it can get electrocuted. Answer: Powdered coal is burnt at high temperature which further turns water into steam. Bridges and automobiles are prevented from rusting by plating them with zinc. Electric eels use electricity to ward off enemies. Join the free ends of two wires momentarily. Now connect one free end of the wire to the terminal of a battery. Question 2. Does lemon juice or vinegar conduct electricity? Give three applications of chemical effect of current. Electricity was first used in homes for lighting. Question 4. Answer: Is it safe for the electrician to carry out electrical repairs outdoors during heavy downpour? Our bodies use electricity to communicate including telling our heart to keep beating. Uses of Electroplating. Question 8. Activity 1 (NCERT Textbook, Page 173) Join the free ends of the tester together fora moment. The seawater contains a huge amount of salts in comparison to drinking water, hence the seawater is a better conductor of electricity and it produces a stronger magnetic field in the wire and hence deflects the compass needle more. (a), Question 4. Static electricity, which doesn't move from one place to another and stays in the place it was created. Oxygen bubbles are formed on the electrode connected to the positive terminal of the battery and hydrogen bubbles are formed on the other electrode. [NCERT]. (a) conduction Electrical energy: The energy produced due to the flow of charge is called electrical energy .it is used widely in electric appliances. This process is known as electroplating. Test. For example, an RV running off of electric heat will use more electricity than an RV running off of propane. So, the fire¬men shut off the electric supply before spraying water to save themselves and other people from electrocution. Protection of the surface of bases metals which corrode for e.g., iron is plated with chromium. Question 17. Why electric fires are extinguished with either using CO 2 extinguisher or mud but not water? Answer: The bulb does not glow in the set-up shown in figure. To her surprise she found that the compass needle showed deflection. When electric current is passed through copper sulphate solution, the copper sulphate breaks up into copper and sulphate ions. Question 3. Electrical charge. (a) conductor This is the Volvo VRN Electric, the company's first electric class-8 truck. Question 8. Answer: Question 6. Question 11. Question 4. Answer: Gravity. 14.1. Question 3. The bulb does not glow because distilled water is an insulator, since it does not have dissolved salts. Chemical Effects of Electric Current Class 8 Extra Questions Higher Order Thinking Skills. [NCT 2011] On passing electric current through the conducting solution of lemon juice and water, chemical reaction takes place. Explain how it can be used for writing. On the other hand the loss of copper from the solution is regained from the impure copper rod which is attached to the positive terminal of the battery. Question 5. Liquid A is a better conductor than liquid B. Electricity is a part of our daily life. Chemical effects of electric current are used in the working of _____ (a) Electrolytic cells (b) Galvanic cells (c) Electrochemical cells (d) None of these. Why ? Our bodies use electricity to communicate including telling our heart to keep beating. Write its one use. (a) magnetic energy into chemical energy Chromium has a good shine, it resists scratches and is corrosion resistant. The filament of the bulb is heated due to current and then it glows. It is concluded that when electric current is passed through the copper sulphate solution, copper sulphate dissociates into copper and sulphate. The writing appears on the paper. Question 16. Answer: What is the disadvantage of electroplating done in the factories ? (a) acids, bases, salts Name three liquids, which when tested in the manner shown in Fig. In this activity the bulb glows which shows that lemon juice and vinegar both conducts electricity, hence they are good conductors of electricity. Hydroxyl ions (OH )move towards the anode and oxygen is collected on it. Question 12. There are specific disposal guidelines for environmental protection. Classify the following liquids into conductors and insulators : lemon juice, , distilled water, tap water, milk. Answer: Answer: Place a small compass needle inside it. The disposal of the used conducting solution after electroplating is hazardous and can cause environmental pollution. Question 8. Answer: The longer lead (leg) from the LED should be connected to the positive terminal of the battery and the shorter lead to the negative terminal of the battery. Flashcards. The iodide ions (I- ) react with starch to turn blue black. Now test if the tester is working or not. Electric Current: The flow of electrons in any material is termed as an electric current. Wait for 3-4 minutes. The most extensive use of gold plating is on jewellery and watch cases. Heat energy: It is the energy due to the motion of molecule. Pour a cupful of water in a glass/ plastic bowl. [NCERT] Iron is a strong metal used for making bridges. Good Conductors of Electricity: The materials which allow the current to pass through them are known as good conductors. Question 10. Can you think of the possible reasons? Question 1. 14.6. (iv) conducting properties of liquid cannot be compared in this manner. It can cause electrocution, as water is a good conductor of electricity. Refining of metal are for obtaining pure metal. and ………….. Take 250 ml. Question 5. Question 7. Electrolysis is the breaking up of a compound from its solution on passing electric current through the electrolyte.