Access to the AP 7th Class Science Study Material 10th Lesson Electric Current and its Effects Questions and Answers are aligned with the curriculum standards.
AP 7th Class Science 10th Lesson Electric Current and its Effects Questions and Answers
AP Board Solutions Class 7 Science Chapter 10 Electric Current and its Effects
Exercise
Question 1.
Draw in your notebook the symbols to represent the following components of electrical circuits connecting wires, switch in the ‘OFF’ position, bulb, cell, switch in the ON position and battery.
Answer:
Question 2.
Draw the circuit diagram to represent the circuit shown in Figure.
Answer:
Question 3.
Figure shows four cells fixed on a board. Draw lines to indicate how you will connect their terminals with wires to make a battery of four cells.
Answer:
Question 4.
The bulb in the circuit shown in Figure does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.
Answer:
Question 5.
Name any two effects of electric current.
Answer:
Two effects of electric current are :
- Magnetic effects of electric current.
- Heating effects of electric current.
Question 6.
When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north – south position. Explain.
Answer:
The needle gets deflected when it is kept near a current carrying wire due to the magnetic effect of the current. The needle of the compass is made up of a thin magnet, and when it comes in contact with the current carrying wire, which also acts like a magnet then the like poles repel each other and opposite poles attract each other. Therefore, the needle get deflected.
Question 7.
Will the compass needle show deflection when the switch in the circuit shown by Figure is closed ?
Answer:
No, the needle will not show any deflection when switch is closed as there is no source of electric current such as cell or battery in the circuit.
Question 8.
Fill in the blanks :
a) Longer line in the symbol for a cell represents its ———– terminal.
b) The combination of two or more cells is called a ———–
c) When current is switched ‘on’ in a room heater, it ———–
d) The safety device based on the heating effect of electric current is called a ———-
Answer:
a) positive
b) battery
c) becomes red hot and emits heat
d) fuse
Question 9.
Mark ‘T’ if the statement is True and ‘F it is False:
a) To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell. (T/F)
b) When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks. (T/F)
c) An electromagnet does not attract a piece of iron. (T/F)
d) An electric bell has an electro-magnet. (T/F)
Answer:
a) False – To make a battery of two cells, the negative terminal of one cell is connected to the positive terminal of the other cell and not to the negative terminal.
b) True
c) False – An electromagnet attracts a piece of iron.
d) True
Question 10.
Do you think an electromagnet can be used for separating plastic bags from a garbage heap ? Explain.
Answer:
No, the plastic bags do not get attracted by the magnet, so they cannot be separated by an electromagnet. Plastic bags are not the magnetic material. Only magnetic materials like iron get attracted to the electromagnet.
Question 11.
An electrician is carrying out some repairs in your house. He wants to replace a fuse by a piece of wire. Would you agree? Give reasons for your response.
Answer:
No, I would not agree because an ordinary wire cannot replace fuse wire.Wires in the fuses have specific melting points.They melts on the passage of high current, thus breaking the circuit and preventing possible fires.
Question 12.
Zubeda made an electric circuit using a cell holder shown in figure, a switch and a bulb. When she put the switch in the ‘ON’ position, the bulb did not glow. Help Zubeda in identifying the possible defects in the circuit?
Answer
Possible reasons are as follows :
- The bulb may be fused or defective.
- Cells are not connected properly.
- There may be loose connections.
- The switch is not functioning well.
- The cells are dried up ie. the power of the cell has been exhausted.
Question 13.
In the circuit shown in Figure
i) Would any of the bulb glow when the switch is in the ‘OFF’ position?
ii) What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position ?
Answer:
i) No, none of the bulb will glow when the switch is in the ‘OFF position, since the electric circuit is not closed.
ii) Bulb will glow simultaneously.When the switch is moved to the ‘ON’ position, then all the bulbs will glow at once. This is because they are all connected to the same battery and switch.
Questions given in the lesson
Page No. 60
Question 1.
Paheli and Boojho wonder whether the batteries used in tractors, trucks and inverters are also made from cells. Then why is it called a battery? Can you help them to find the answer to this question?
Answer:
Cell is the smallest unit of battery. Combination of two or more cells is called a battery. The batteries used in tractors, trucks and inverters contain about 4-6 cells.
Page No. 64
Question 2.
Boojho could not see elements in an electric iron. Paheli told him that electrical appliances, such as immersion heaters, hot plates, irons, geysers, electric kettles, hair dryers have elements inside them. Have you ever seen the element in any appliance?
Answer:
Yes, we have seen the element inside many other electric equipments like electric heaters, electric kettles etc. The element is in the coiled form, it takes the current from the source and heats up the coil inside it. Thus, it serves the purpose of heating up due to electric current.
Extended Learning – Activities and Projects
Question 1.
Set up the circuit shown in Figure again. Move the key to ‘ON’ position and watch carefully in which direction the compass needle gets deflected. Switch ‘OFF the current. Now keeping rest of the .circuit intact, reverse the connections at the terminal of the cell. Again switch ‘on’ the current. Note the direction in which the needle gets deflected. Think of an explanatiop.
Answer:
When the connection of cell is reversed, the compass needle moves in opposite direction. This shows that the polarity of the magnet depends on the direction of low current.
Question 2.
Make four electromagnets with 20, 40, 60 and 80 turns. Connect them one by one to a battery of 2 cells. Bring the electromagnet near a box of pins. Count the number of pins attracted by it. Compare the strengths of the electromagnets.
Answer:
The electromagnet with 80 tonnes will attract the maximum number of pins, followed by that of 60 turns, then 40 turns, and finally 20 turns will attract the least number of pins. This is because the strength increases with the increase in the number of turns in the coil.
Question 3.
Using an electromagnet, you can make a working model of a railway signal as shown in Figure.
Answer:
Take a cardboard and make a hold into it. Attach the carbon hole to a stand.Tie a thread to one end of the cardboard and tie an iron nail to the thread. Make an electromagnet and rotate the coil of wire on it. Connect the wire to a battery and a key. In this way, a railway signal can be made.
Question 4.
Visit an electric shop. Request a electrician, to show you the various types of fuses and MCB and to explain how they work.
Answer:
The various types of MCB are :
- MCB
- MCCB
- ACB
- VCB
- RCCB
The various types of fuses and MCB are:
- AC fuses: AC fuses are little bit smaller than the DC fuses because in AC the voltage with 60 Hz changes its amplitude from 0 to 60 times every second.
- DC fuses: When the metallic wire melts, heat generated due to large current, an arc is produced. DC fuses are bigger than AC fuses to increase the distance between the electrodes. So that the arc is reduced.
- One time use only fuses : These types of fuses are used once only. When the high current flows, they melt and gets burnt out. These fuses are replaced manually.
- Cartridge fuses : These types of fuses have plastic body and two metal caps for fitting in the socket. These are used generally in automobiles.
- Resettable fuses: These fuses can work multiple times. They open the circuit when high current flows through it and after some time they again connect the circuit.
Activities
Activity 10.1 Page No : 60
Question 1.
i) Do you remember that the bulb glows only when the switch is in the ‘ON’ position?
Answer:
i) The bulb glows as soon as the switch is moved to the ‘ON’ position.
ii) Fig. 10.9 shows another circuit diagram. Is it identical to the circuit diagram shown in Fig. 10.8?’In which way is it different? Would the bulb glow in this electric circuit?
Answer:
No. Fig. 10.9 is not identical to Fig. 10.8.
Fig. 10.8 have switch in ‘OFF’ position as contrast to Fig. 10.9 which switch in ’ON’ position. No. the bulb would not glow because bulb glows only when the switch is in the ‘ON’ position and the electric circuit is closed.
Activity 10.2 Page No : 62
Question 2.
Take an electric cell, a bulb, a switch and connecting wires. Make an electric circuit as shown in Fig. 10.9. This activity has to be done using only one cell. Keep the switch in the ‘OFF’ position. Does the bulb glow? Touch the bulb. Now move the electric switch to the ‘NO’ position and let the bulb glow for a minute or so. Again touch the bulb. Do you feel any difference ? After moving the switch back to the ‘OFF’ position, touch the bulb again.
Answer:
Aim : To show the heating effect of electric current.
Materials required : Electric cell, small torch bulb, switch, connecting wires with insulation removed from its end and adhesive tape.
Procedure :
- Connect the electric cell to the torch bulb along with the switch with the help of connecting wires and tape.
- Keep the switch in the ‘OFF’ position.
- Touch the torch bulb.
- Put the switch in the ‘ON’ position.
- Allow the bulb to glow for a minute.
- Touch the bulb carefully.
Observations: We observe when the switch is in ‘OFF’ position, the bulb is not warm, but when it is ‘ON’ position, the bulb feel warm.
Conclusion : From the above activity, we can conclude that when the electric current flows in the wires, the bulb becomes warms. Hence, current has heating effects.
Activity 10.3 Page No: 64
Question 3.
Make a circuit’as shown in Figure. Take about 10 cm long piece of nichrome wire and tie it between the nails. (You can get nichrome wire from an electric repair shop or you can use a piece of discarded coil of an electric heater.) Touch the wire. Now switch on the current in the circuit by moving the switch to the ‘ON’ position. After a few seconds touch the wire. Switch off the current. Touch the wire again after a few minutes.
Answer:
Aim : To show the heating effect of electric current.
Materials required : Nichrome wire, iron nails, thermocol sheet, switch, cell.
Procedure :
- Two nails are placed on a thermocol and are connected with a cell and a switch.
- A nichrome wire of 10 cm long is tied between the nails.
- Touch the wire.
- Now switch on the current in the circuit by moving the switch to the ‘ON’ position.
- After a few seconds touch the wire.
- Switch off the current.
- Touch the wire again after a few minutes.
Observations : We observe when the switch is in the ‘OFF’ position, no current flows through the circuit.When the switch is turned ‘ON’ the electric current flows through the circuit, making the wire hot. So, when the wire is touched at this time, nothing is felt.
Conclusion: From the above activity, we can conclude that when the switch is turned ‘ON’ the electric current flows through the circuit, making the wire hot.This is called as the heating effect of the electric current.
Activity 10.4 Page No: 68
Question 4.
Make the circuit we used for Activity 10.3 again. However, replace the cell with a battery of four cells. Also, in place of the nichrome wire, tie a thin strand of steel wool. (The steel wool is commonly used for cleaning utensils and is available in grocery shops.) If there are any fans in the room, switch them off. Now pass the current through the circuit for some time. Observe the strand of steel wool carefully. Note what happens. Does the strand of steel wool melt and break ?
Answer:
Aim : To show the working of a fuse.
Materials required : Four celled battery, steel wool, two nails, a sheet of thermocol, switch, bulb and connecting wires.
Procedure :
- Fix two nails about 10 cm apart on the sheet of thermocol.
- Tie a thin Jstrand of steel wool between the two nails.
- Connect the nails to the two terminals of four celled battery through a switch and a battery by using connecting wires.
- If there are any fans in the room, switch them off.
- Now pass the current through the circuit for some time.
- Observe the strand of steel wool carefully.
Observations: We observe after a few seconds, the thin strand of steel wool melts and breaks and the bulb goes off. Actually, instead of steel wool is like a fuse wire here.
Conclusion : From the above activity, we can conclude that when a large current passes through the thin strand of steel wool, a lot of heat is produced in it due to the heating effect of current. This heat melts the thin strand of steel wool and breaks it. cutting off the flow of current in the circuit. This is how a fuse works in the household electronic wing.
Activity 10.5 Page No : 70
Question 5.
Take the cardboard tray from inside a discarded matchbox. Wrap an electric wire a few times around the cardboard tray. Place a small compass needle inside it. Now connect the free ends of this wire to an electric cell through a switch.
Note the direction in which the compass needle is pointing. Bring a bar magnet near the compass needle. Observe what happens. Now. while watching the compass needle carefully, move the switch to the ‘ON’ position. What do you observe Does the compass needle deflect? Move the switch back to the ‘OFF’ position. Does the compass needle come back to its initial position? Repeat the experiment a few times. What does this experiment indicate ?
Answer:
Aim : To show the effect of current on a compass needle.
Materials required: Card board tray, electric wire, compass needle, electric cell, switch, bar magnet.
Procedure:
- Take the cardboard tray from inside a discarded matchbox.
- Wrap an electric wire a few times around the cardboard tray.
- Place a small compass needle inside it.
- Now connect the free ends of this wire to an electric cell through a switch as shown in Figure.
- Note the direction in which the compass needle is pointing.
- Bring a bar magnet near the compass needle.
- Observe what happens.
- Now, while watching the compass needle carefully, move the switch to the ‘ON’ position.
Observation: We observe when the switch is ‘ON’ position the compass needle deflects. When the switch is in ‘OFF’ position, the compass needle comes back to the original position.
Conclusion: From the above activity, we can conclude that compass needle is a tiny magnet and it points in north-south direction. When the magnet comes close to it, the compass needle get deflected. Also when electric current flows nearby needle gets deflected.When electric current flows, through wire, wire behaves like magnet. This is magnetic effect of electric current.
Activity 10.6 Page No: 72
Question 6.
Take around 75 cm long piece of insulated (plastic or cloth covered or enamelled) flexible wire and an iron nail, say about 6 -10 cm long. Wind the wire tightly around . the nail in the form of a coil. Connect the free ends of the wire to the terminals of a cell through a switch. Place some pins on or near the end of the nail. Now switch on the current. What happens? Do the pins cling to the tip of the nail ? Switch off the current. Are the pins still clinging to the end of the nail ?
Answer:
Aim: To make an electromagnet and to show that it attracts iron.
Materials required : Long piece of copper wire, iron nail, electric cell, switch, iron pins.
Procedure:
- Take around 75 cm long piece of wire copper wire.
- Wind the wire tightly around the nail in the form of a coil.
- Connect the free ends of the wire to the An electromagnet terminals of a cell through a switch as shown in Figure.
- Place some pins on or near the end of the nail.
- Now switch on the current.
Observations : We observe when two ends of the wire are connected to the cell, the current is flowing through the coil. As a result, the pins get attracted to the electromagnet. When we disconnect the wire, the pin falls off.
Conclusion : From the above activity, we can conclude that the iron nail behaves like a magnet which attracts the pins towards it. It will happen when the current flows through the wire, but if we disconnect the circuit, the iron loses its magnetic property.