Rajasthan Board RBSE Class 8 Science Chapter 11 Effects of Electric Current
RBSE Class 8 Science Effects of Electric Current Intext Questions and Answers
Page No 119.
How does sound, heat, etc. produced due to electric flow ?
1. When electric current flows through a conducting wire, the wire becomes hot. This is heating effect of electric current. Due to this effect heat is produced.
2. There are so many turns of insulated copper wire, wrapped on the iron-core of coil. There is an iron strip attached near to coil and a strike also attached to it. Iron strip placed nearby contact screws. On passing current through this coil due to magnetic effect of electric current coil becomes electromagnet. Because of this iron strip attracts towards the coil and striker attached to the iron strip make a collision with bell and sound is produced.
Page No 120.
After plug in key, the electric current flows through the circuit. Now, touch the wire. Why does the wire heat up?
When electric current flows through a conducting wire, it becomes hot due to the heating effect of electric current.
Page No 121.
The exces eletric currents passes through electric circuits due to short circuits. As a result the appliances are become not and catch fire and may because for fire accident. What do we do to protect from an accident or damage to an appliances?
To save electrical appliances an equipment should be used in series with the electrical circuit such that when current increases over limiting value, then it melts and current stops. This – equipment is called as fuse.
Page No 122.
How does fuse works?
There is increase in temperature when an electric current above safe value flows in a circuit of exceed limiting value. This melts the fuse wire and circuit breaks,
Page No 123.
Can magnetic needle being deflected by an electric current?
Yes, when electricity is passed through a conducting wire, then it behaves like a magnet. This is called magnetic effect of electric current. Due to this effect there is deflection in the – magnetic needle.
Page No 126.
Does the pure water conduct electric?
No, because it is neutral in nature.
RBSE Class 8 Science Effects of Electric Current Text Book Questions and Answers
Choose the correct Answers:
Electric bell is based on which electric current effect?
(a) thermal effect
(b) magnetic effect
(c) chemical effect
(d) joule effect
(b) magnetic effect
Which is the object used to collect the magnetic matter from scrape?
(b) electric cell
(d) immersion rod
Which in the following solutions not pass electric current ?
(a) copper sulphate
(b) silver nitrate
(c) pure water
(d) salted water
(c) pure water
Which is not a component of electric bell –
(a) strip of iron
(c) contact nut
(d) magnetic fiddle
(d) magnetic fiddle
Fill In the blanks with suitable words:
- The long line represents ……………………. and short line represents ……………………. terminal of electric battery’s symbol.
- The safety device based on heating effect of electric is called …………………….
- In battery, the plate connected to positive terminal is called ……………………. and to negative terminal is called
- The magnetic effect of electric current is discovered by …………………….
- positive (+), negative ( – )
- Amide, cathode
- Scientist named Oersted
Short Answer Questions:
What is the fuse?
Fuse is a safety device in the form of a wire which is made up of mixture of copper, zinc, tin, etc. whose melting point is lower than the melting point of appliances and the wires used in electrical circuits. When the circuit is overloaded or during a short circuiting the fuse wire melts and breaks; and hence the current stops flowing in the circuit. Thus, the possible harm is avoided.
Write any three applications of electromagnet.
- To separate magnetic substances from junk scrap of garbage, electrical magnet is used.
- In electric bell, electrical magnet is used.
- To pick up heavy iron items, electrical magnet crane is used.
What is thermal effect of electric current? Write down the names of any four appliances based on this effect.
Heating Effect of Electric Current:
When electric current flows through a conductor wire, it becomes hot. This is known as heating effect of electric current. Following are the nines of devices based on healing effect of electric current.
- Electric oven
- Electric toaster
- Electric iron
- Electric bulb
Long Answer Questions:
Make a diagram of electric bell and explain its working system.
Structure of Electric Bell:
As shown in the given diagram following are the important parts of electric bell.
- Iron sheet
- Connecting screw
In coil, an iron core is wrapped by many circles of electrical resistance copper wire. There is an iron strip placed near this coil. One end of this strip is attached to a hammer, this strip remains is close contact with a nearby contact screw.
When switch on, then electric current tows in the coil and due to the magnetic effect of electric current coil becomes an electrical magnet. But lo this the iron strip gets attracted towards the coil and the hammer connected to the iron strip beats the bell and produces sound. When electrical magnet attracts the iron strip towards il, then the strip loses its contact with the screw. which breaks the circuit. Due to this, the how of electric current stops in the coil. In this state, coil does not behave as electrical magnet. Then, the iron strip comes hack to its original position as the attraction of coil on iron strip ceases. Now, again electric current starts flowing in the coil and, again hammer beats the hell. This process is repeated.
What is chemical effect of electric current? Explain the process of electroplatting.
Chemical Effect of Electric Current:
If electric current flows in any conducting Solution. then il dissociates into its components. This is known as chemical effect of electric current.
The process of plating or coaling any substance with the help of electricity with a known metal is known as electroplating. In the process of electroplating. a breaker is taken containing metal which is used for coaling in the form of its salt solution and same metal anode terminal is made. Metal which is to he coated is used as cathode ( – ) terminal. Now, electric current is allowed to flow for a sufficient period of time. When electric current flows: positive metal ions get displaced from salt solution and are coated over cathode and positive metal ions get released from anode and are mixed in salt solution, This is how a known metal coating is done.
RBSE Class 8 Science Effects of Electric Current Important Questions and Answers
Which of the following device is based on healing effect of electric current?
(a) Electric Oven
(b) Electric Toaster
(c) Electric Press
(d) All of these
(d) All of these
Now a days what is used in place of fuse –
(d) None of these
Which of the following uses electromagnet?
(a) Electric Bell
(b) Electric Crane
(d) All of the above
(d) All of the above
Distilled water is of electricity.
(d) None of these
Which marked electric fuse should we use?
Which of following is used to extract pieces of magnetic material fallen into eye accidentally.
(a) Electric magnet
(b) Electric cell
(a) Electric magnet
The process of plating of a required metal on a substance by electric is called –
(a) Electric flow
(b) Electric heat
(c) Electric clasping
Fill in the blanks:
- The electric circuit …………………… on melting of fuse wire. (break/join)
- Now a days …………………… is used in place of a fuse. (MCB/ISI)
- To lift heavy iron objects …………………… is used. (Electromagnetic crane/crane)
- Some liquids are good conductor of electricity while some are …………………… (Insulator/less conducting)
- To prevent iron from …………………… a zine layer is coated. (rust/polish)
- Conducting wire becomes hot when electric current flows, it shows …………………… effect of electric current. (heating/magnetic)
- Fuse is placed in …………………… of electric circuit. (series/parallel)
- Electromagnetic crane
- less conducting
State True or False:
- We should not plug many devices in a single socket. ( )
- Now a days fuse is use in place of MCB. ( )
- Electromagnet is used in telephones.( )
- Electric oven is based on chemical effect of electric current. ( )
- Electric bulb is based on magnetic effect of electric current. ( )
- Acid, base and salt solutions are good conductor of electricity. ( )
- To protect from short circuit, fuse is used in the electrical circuit. ( )
- Electroplating process is based on heating effect of electric current. ( )
Math the Column –
Match the following correctly:
Very Short Answer Type Questions:
Write the names of electric devices used in our daily life.
Electric iron, electric heater, electric oven. electric bulb, electric bell, electric toaster etc. are used in our daily life.
What is heating effect of electric current?
When electric current flows through a conducting wire. the wire becomes hot. This is called heating effect of electric current.
Naine some devices based on heating effect of electric current.
Electric oven, electric toaster, electric iron, electric bulb, electric heater etc. are the devices based on heating effect of electric current.
Name the three holes in the socket of house?
- Electrified wire or phase
- Neutral or Isolated
- Earthing wire.
What is the value of voltage on neutral wire?
The value of voltage on neutral wire is
What is short circuit?
When phase wire and neutral wire accident comes in contact with each other, then it is called short circuit.
What is overloading ?
Cause of excess current is plug too many things into a socket. This is called as overloading.
What is fuse ?
Electric fuse is a safety device connected in series, having a wire of alloy of copper, zinc, tin and other alloys. When the current flowing through the circuit exceed a safe limit the wire melts and break the circuit.
Where the fuse wire is placed ?
Fuse wire always placed in porcelains or in insulated material cartage.
Fuse wire is made up of which material?
Generally fuse wire is made of alloy of copper, zinc, tin.
What is magnetic effect of electric current?
Magnetic Effect of Electric Current: When the electric current flows through a conducting wire; then the conducting wire behaves as a magnet. This is known as Magnetic Effect of Electric Current.
Name the various elements of an electric bell.
An electric hell has six main elements –
- Iron strip
- Contact screw
Coating of a desired unreactive metal on some other metal with the help of electricity. This process is called electroplating.
What is the chemical effect of electric current?
The process by which some liquid carries current through them and dissociates into its ions, is called Chemical Effects of Electric Current.
Name some objects which are electro plated?
- Jewellery coated with gold and silver.
- Some parts of car, motorcycles, handles of bathroom taps, rim of wheels etc.
- Coating of zinc on iron.
Short Answer Type Questions:
Write the uses of electromagnet.
- Electromagnets are used to short out magnetic substances from garbage.
- Electromagnets are used by doctors to remove small iron pieces from the eye of the patient.
- it is used as magnetic crane lo lift heavy iron objects.
Explain how distilled water can be made conducting electricity.
Take a clean and dry plastic beaker, and fill it with distilled water. By using a tester, it will be acknowledged that distilled water does not conduct electricity. Take a pinch of salt and dissolve it in distilled water. Test it with tester. It will be found that it conducts electricity.
Why do we use fuse wire in electric circuit?
If there is excessive electric current in the circuit due to short circuit or few any other reason, the equipment of the house can become hot and catch fire or may cause lire accident. Therefore, we use fuse wire in hie electric circuit to avoid accidents and to prevent the damage of electricity appliances. Effect of stream of value over the value specified in the circuit increases the heat of the fuse wire, so that the wire metals and the circuit breaks.
What may be causes of short circuit? Write any two causes.
1. When more than limit range current flows in the circuit then wire becomes hot, due to which plastic covering of the wire melts, as a result phase and neutral come in contact to each other and short circuit takes place.
2. Plastic covering on old wires, weaken and break then short circuit occurs.
Write the names and uses of any four instruments based on heating effect of electric current.
Four instruments based on the heating effect of electric current –
- Electric oven – To cook food in the kitchen.
- Electric toaster – To roast the bread.
- Immersion rod – To heat/boil the water.
- Electric press – To press the clothes.
Write few chemical effects of electric current. .
- Chemical activities take place when current passes through a conducting solution.
- Due to chemical effect, gas bubbles can he found on electrodes.
- Deposition of a metal can take place on electrodes. Colour of electrolytes can also change.
When the free ends of a tester are dipped into a solution, the magnetic needle shows deflection. Can you explain the reason?
When the free ends of a tester are dipped into a solution electric current flows in the solution. Due to how of current in the solution the magnetic needle deflects.
Name three liquids, which when tested in the manner shown in Fig., may cause the magnetic needle to deflect.
- Lemon juice
- Sail solution
- Copper sulphate solution.
How does the fuse work?
If the supply of current flowing in the circuit is above the safety level, then the temperature of the fuse wire increases. This melts the fuse wire and breaks the circuit. Fuse wires are generally kept in cartage of porcelain.
Earthing is a safety measure. How?
Earthing is a safety device which ensures if any metal coating of any electrical equipment is touching with phase wire. then man using that equipment does not receive a shock.
Explain the applications of electroplating.
Following are the main applications of electroplating –
- Jewellery is coated with gold and silver through electroplating.
- Electroplating is done in some car parts, bathroom tap, gas burner, cycle handle, rim of wheels, etc. which are plated with nickel and chromium.
- To protect iron from rusting zinc is plated.
Identify the conductors and insulators of electricity among the following –
- Distilled water
- Lemon juice
- Tap water.
- Distilled water – Insulator
- Lemon juice – Conductor
- Vinegar – Conductor
- Tap water – Conductor.
Long Answer Type Questions:
Define and explain heating effect of electric current with suitable diagram. Write the name of an appliance based on this effect.
Heating effect of electric current – When the electric current passes through the conducting wire. ¡t becomes hot. It is called healing effect of electric current. Heating effect of electric current.
Take thin nichrome wire and wrap it on pencil. Connect the one end of nichrome wire with cell and other end with key. Connect the electric circuit. After plug in key, the electric current flows through the circuit. Now, touch the wire after some time. We observe that the wire heat up because nichrome is a good conductor of electricity. The wire gets hot when an electric current passes through ¡t due to the heating effect of the electric current.
What do you mean by magnetic effect of electric current? Explain with suitable diagram. Write name of an appliance based on this effect.
Explain the magnetic effect of current with help of diagram. Write the name of two apparatus working on this principle. Explain the working of electric bell by drawing its labelled diagram.
Magnetic effect of electric current – When an electric current flows through the conductor, then conducting wire behaves like magnet. It is called the magnetic effect of electric current.
Take the cardboard piece and make two holes at a few distance to each other. Put a magnetic needle or compass. Now, adjust the cardboard in such a way that we see the compass needle beneath the wire from top view. On connecting free ends of wire to the cell electric current starts flowing. In such situation conducting wire acts as magnet and the magnetic needle deflects. This effect is magnetic effect of electric current.
electric cell, electric bell, telephone, telegraph. etc.
For working and diagram of electric bell see Long Ans. [ Text book Questions].
What precautions should be taken to check the fuse wire connected In main line? What is miniature circuit breaker (MCB)? Draw its diagram also.
1. Do not make an effort to check the fuse wire connected in main line on yourself. It may be dangerous. To know about it. You may visit Lo electric circuit repair shop and compare the damage fuse wire with new fuse wire. We should use ISI marked fuse wire. Do not use any metal strip of wire in place of fuse wire.
2. Miniature circuit breakers (MCBs) – These days Miniature circuit breakers (MCBs) are used in place of fuses. These are switches which automatically turn off when current in a circuit exceeds the safe limit. When we turn ON them, then circuit is once again completed.
3. Diagram of MCB
How can we make a tester using magnetic effect of electric current? Draw Its diagram also? How electricity conducts through liquids?
1. Making tester –
Take empty match boxes as tray and put a magnetic needle. Now wrap the enamelled copper wire on it. Connect the one end of wire with one battery terminal and leave other end free. Connect the second terminal of battery with another wire and leave it end free too. Now, connect these two free ends then magnetic needle deflects. In this way tester with two free ended wires is ready.
2. Conductance of electricity in liquids. Liquids also conduct electricity hut all types of liquid does not conducts electricity. For the conductance of electricity in liquids. they must he solutions of acids, bases and salts. This is the reason why distilled water does not conducts electricity, as il has not such nature, i.e. acidic, basic or salty.
What is fuse ? What ¡s its work ? How does it works ? Explain its properties diagrammatically.
Fuse – To save a electrical appliances an equipment is used to the series with the electrical circuit such that when current increases over limiting value, then it melts and current stops. This equipment is known as fuse. At present tune a specific fuse is fitted internally in costly electronic instruments like T.V., fridge etc.
- it saves the domestic electric equipments from damage.
- It prevents short circuiting.
How it works –
There is increase in temperature when an electric current over safe value flows in a circuit of exceed limiting value. This melts the fuse wire and the circuit breaks.
- Fuse wire is always plugged in porcelains or insulated material cartage.
- Generally fuse wire is made of alloy of copper. zinc, tin etc.
- Its melting point is less than the melting points of devices used in the electric circuit.
- Due to its low melting point, when the current in the circuit exceeds, it melts and break the circuit.
What is short circuit? Explain its cause and damages. What is its protection?
Short Circuit –
When the plastic insulation of live wire and neutral wire become worn due to which they get bare (naked) and accidentally comes in contact, then it is called short-circuit. During short-circuit a large amount of electric current flows, and domestic appliances produces a lot of heat and catches fire. One of the reason of flowing of excessive current in the circuit is to attach more than one equipment from a single socket because of which the circuit gets overloaded. Thus we should not plug more than one equipment from the same socket.
Causes of short circuit –
1. When the supply of electric current is more than the safety level, then the wires become hot and the plastic covering on them melts and the phase wire and neutral wire join together causing short circuiting.
2. When plastic covering of old wires breaks, then it causes short circuit. Damages – Due to short circuit the current in the circuit exceeds the limit because of which the instruments may heated up and catches fire and a lire accident can cause.
To save electrical appliances from damage, such kind of device should he used in the circuit, which gets melted and stop the electric current in the circuit when the unit of current reaches above the safety level, ibis device is known as fuse.
How is electromagnet prepared ? Explain with diagram? In your opinion what are the applications of electromagnet.
Take 10-15 cm long iron-nail and 50cm long thin insulator covered (enameled) copper wire.
Now at the both end of wire remove the insulated plastic and wrap this wire on the nail. Connect the both open ends of the wire to key and cell as shown in electric circuit. When circuit is off (key is not pressed). then move a pin towards the nail. In this position when there is no current drawn from the cell, then there is no attraction between pin and nail. Now press the key and flow the current in circuit. Move the pin towards nail. When current tows through the wire wrapped on the nail, then nail behaves as magnet. Magnet formed by this type is called as electro-magnet.
Application of electromagnet are as follows:
- Electrotnagnet is used to collect the magnetic materials from the scrape.
- Electromagnet is used by the doctor to draw pieces of magnetic material fallen into eye accidentally.
- Electromagnetic cranes are used to lift heavy iron objects.
Explain the electric socket diagram matically.
There are three types of wire used for electric supply in our houses. When there is no electricity in our house, then you call any electrician to repair, you have seen that electrician at that time check the electric supply with a tester. There are three holes in socket of house. Part of the socket in which there is blink of light on using testers, that is called electrified wire or phase. In domestic circuit phase is mostly red plastic covered wire. Hole near to this phase in which on entering the tester there is no blink of light, that is called isolated or Neutral. On neutral wire voltage is zero, A
black plastic coated wire is used mostly as neutral wire voltage is zero. A black plastic coaled wire is used mostly as neutral wire. ‘The electricity between them is 220 volts. Third wire is earthing wire, which is covered with green plastic. Earthing is the system of connecting the metal casing of on electric appliance with a copper plate buried inside the earth.
What is meant by chemical effect of electric current? Explain with the help of an activity diagramatically. Where does it used?
Explain the chemical effect of current with help of diagram. Write the two applications of this effect. Explain the electroplating method with help of a diagram.
When electric current passes through any conducting solution. Ii dissociates into its constituents. It is called chemical effect of electric current.
Take out carbon rods carefully from two discarded cells. Clean their metal caps with sand paper. Wrap copper wires around the metal caps of the carbon rods and join them to a battery. We call these two rods electrodes. Plate connected to positive terminal of the battery is called anode and plate connected to egative terminal of the battery called cathode. In the symbol of electric cell, the longer line denotes positive terminal and small line denotes negative terminal. Pour a cupful of water in a glass/plastic bowl. Add a teaspoonful of salt or a few drops of lemon juice to water to make it more conducting. Now immerse the electrodes in this solution.
Make sure that the metal caps of the carbon rods are outside the water. Wait for 3- 4 minutes. Observe the electrodes carefully. We will notice some gas bubbles near the electrodes. The passage of an electric current through a conducting solution causes chemical reactions. As a result, bubbles of a gas may be formed on the electrodes. Deposits of metal may he seen on electrodes. Changes in colour of solutions may occur. These are some of the chemical effects of the electric current. Uses – It is used in the electroplating of many utensils and deices.
What is electroplating process ? Write its two uses.
Name the process of gold plating on silver ornaments and also draw a diagram of the process.
Electroplating – Coating of unreactive metal on any other metal with the help of electricity is called electroplating. e.g. Gold plating on the silver jewellery is done by this method.
The reasons for electroplating are –
- Main element is to be protected against corrosion.
- To make it attractive.
- To protect it from scratches.
Method of electroplating –
The substance which is to he coated in connected to negative terminal of the battery and the coating material is connected to positive terminal. The electrolyte is made up of the salt of the metal which is to he coated and both the electrodes are dipped in the solution of electrolyte.
When current flows through it, then The thin layer of anode metal is coated on the object which is acting as cathode.
Why is electroplating useful ? Explain.
We know that in electroplating, a coat metal is plated on another metal object. The plated metal here has some uncreative properties as compared to the metal which is coated, for example – some parts of car, tap of bathroom, handle of cycle, rims of wheels, etc. has a plating of chromium. Chromium is lustrous and prevents corrosion. Since chromium is an expensive metal and therefore, it is not practical to make things with this metal.
That’s why objects arc made up of cheap metals and then arc coated with chromium. Artificial jewellery is made up of cheap metals coated with silver and gold. These look like silver and gold but are very cheap. Cans storing food are made up of iron but are electroplated with tin as it is less reactive then iron so food material does not get spoiled in cans coated with tin. Bridges and self-driven vehicles are made strong by using iron. But iron gets easily corroded and rusted so to protect it, it is coated with zinc by electroplating. In this way electroplating is widely used.