These AP 7th Class Science Important Questions and 10th Lesson Electric Current and its Effects Class 7 Extra Questions will help students prepare well for the exams.
Class 7 Science Electric Current and its Effects Extra Questions
Electric Current and its Effects Class 7 Important Questions
Question 1.
Why is an electric fuse required in all electrical appliand?
Answer:
Electric fuse is required in all electrical appliances to prevent damage from excessive current flow and during short circuit.
Question 2.
What do the long line and the shorter line in an electric cell represent?
Answer:
The longer line represents the positive terminal and the thicker, shorter line represents the negative terminal.
Question 3.
What is the coil of wire in electric devices known as?
Answer:
The coil of wire in electric devices is known as an element.
Question 4.
What are the components of a simple electric circuit?
Answer:
The components of a simple electric circuit are battery, wire, key and bulb.
Question 5.
What is an electric cell?
Answer:
It is a device which produces electric charge because of some chemical reactions.
Question 6.
Where does the needle of the compass point?
Answer:
The needle of the compass points in the North-South direction.
Question 7.
Name the scientist who noticed the magnetic effect of electric current for the first time.
Answer:
Hans Christian Oersted noticed the magnetic effect of electric current for the first time.
Question 8.
Which effect of electric current is utilised in the working of an electric fuse?
Answer:
An electric fuse works on the heating effect of current.
Question 9.
Expand MCB.
Answer:
The full form of MCB is “Miniature Circuit Breakers”
Question 10.
What is electromagnet? Name a device that uses electromagnet.
Answer:
A current carrying coil of an insulated wire wrapped around a piece of iron is called an electromagnet. Cranes uses electromagnet.
Question 11.
What is a circuit diagram?
Answer:
A circuit diagram is a graphical representation of an electric circuit which is the drawn using symbols of different electrical components.
Question 12.
What is a fuse?
Answer:
A fuse is a safety device which prevents the damage is to electrical circuits and possible fires.
Question 13.
On what factors does the heat produced in a wire depends?
Answer:
It depends on the material, length and thickness of wire.
Question 14.
Where can we place the key or switch in the electric circuit?
Answer:
We can place the key or switch anywhere in the circuit.
Question 15.
What do you mean by battery?
Answer:
It is a combination of two or more cells in which the positive terminal of one cell is connected to the negative terminal of the next cell is called a
battery.
Question 16.
What happens when we bring a magnet close to the compass?
Answer:
The needle of the compass shows deflection when we bring a magnet close to it.
Electric Current and its Effects Extra Questions
Question 1.
Name two electric devices for each where
a) heating effect of current is used and
b) magnetic effect of current is used.
Answer:
a) Heating effect of current is used in room heater and geyser.
b) Magnetic effect of current is used in electric bell and cranes.
Question 2.
Can we use the same fuse in a geyser and a television set? Explain.
Answer:
No, we cannot use the same fuse in a geyser and television because a geyser and a television set require a different amount of current. The fuse used in every appliance has some limit to withstand the current flowing through it. So, different appliances have fuses of different ratings.
Question 3.
What are the conditions necessary for an electric current to flow?
Answer:
The necessary conditions for an electric current to flow are as follows :
- A source of electric current (a cell or a battery).
- A conducting material or metal wire.
- An uninterrupted path for the flow of charge.
Question 4.
When does the current to flow through the circuit ? Explain.
Answer:
When the switch is in the on position, and the positive terminal of the battery is connected to the negative terminal of the battery through wires then the circuit is said to be closed and the current flows throughout the circuit.
Question 5.
What are the reasons for excessive currents ?
Answer:
The possible reasons for excessive currents are as follows :
- One reason for excessive currents in electrical circuits is the direct touching of wires. This may happen if the insulation on the wires has come off due to wear and tear.
- The connection of many devices to a single socket may cause overloading in the circuit and thus may lead to possible fires.
Question 6.
Write short notes on heating effects of electric current.
Answer:
When an electric current flows through a wire, the wire gets heated. It is the heating effect of current or when current flows through a metal wire it gets heated up, this is called heating effect of current. E.g: a glowing electric bulb becomes warm. This effect has many applications like Electric Heater, Light Bulb etc.
Question 7.
Give two methods by which we can increase the strength of magnetic field produced by a circular coil carrying current?
Answer:
The two methods by which we can increase the strength of magnetic field are as follow:
- By increasing the number of turns of wire in the coil.
- By increasing the current flowing through the coil.
Question 8.
Explain the formation and uses of battery.
Answer:
A combination of two or more cells in which the positive terminal of one cell is connected to the negative terminal of the next cell is called a battery. It supplies electric current. To identify the positive and negative terminals, they are denoted as + and – respectively. These batteries are used in many devices, such as torch lights, mobile phones, calculators and even automobiles.
Question 9.
Differentiate between an open and a closed circuit.
Answer:
Open circuit : The electric path which starts from positive terminal of a cell or battery but is broken at some point, is called an open electric circuit. Current does not flow from.such a circuit and the switch is in ‘OFF’ position.
Closed circuit : The electric path which starts from the positive terminal of a cell or battery ends at its negative terminal, without any break, is called a closed electric circuit. Current flows in the circuit and the switch is in ‘ON’ position.
Question 10.
Why do we generally represent an electric circuit by its circuit diagram?
Answer:
We generally represent an electric circuit by its circuit diagram because it is much easier to draw circuit diagrams using symbols.
Question 11.
Write the functions of an MCB.
Answer:
The functions of an MCB are :
We can use an MCB in place of a fuse. It automatically breaks the circuit if it crosses the safe limit of electricity and prevents short circuits and other damage. An MCB can be handled manually.
Question 12.
If the current flows through wire, does the wire behave like a magnet?
Answer:
When the current flows through any wire, a magnetic field is developed around that wire or coil and it behaves like magnet. It can be analysed by placing a magnetic compass around the wire, it will show deflection of the needle.
Question 13.
If we connect more cells in the circuit, then what will happen?
Answer:
If we connect more of cells in the circuit, then the nail will attract more pins. It is due to the reason that the current flowing through the wire wound on the nail will get increase which in turn will increase the strength of the electromagnet.
Question 14.
Write the differences between a bar magnet and electromagnet.
Answer:
The differences between bar magnet and a electromagnet are as follows :
| S.No. | Electromagnet. | Permanent magnet |
| 1) | It is usually made up of soft materials. | It is usually made up of hard materials. |
| 2) | Removal of magnetic properties is temporary. | Once magnetic properties are lost, it becomes useless. |
| 3) | The magnetic properties that are displayed when current is passed through it. | Magnetic properties exist even when no current is there. |
| 4) | The poles of this kind of magnet can be altered with the flow of current. | The poles of this kind of magnet cannot be changed and are fixed. |
| 5) | The strength is adjusted depending upon the amount of flow of current. | The strength depends upon the. nature of the material used in its creation. |
Question 15.
On what does the strength of an electromagnet depend upon?
Answer:
The strength of an electromagnet depends upon the amount of current flowing through the coil and the number of turns of copper wire in the coil.
Extra Questions of Electric Current and its Effects Class 7
Question 1.
What are electric fuses? Why are they called safety devices?
Answer:
The wires made up of special materials which melt quickly and break when large electric currents are passed through them are known as electric fuses. There is a maximum limit of electric current that can safely flow through a circuit.
If by accident the current exceeds this safe limit, the wires may become overheated and may cause a fire. If a proper fuse is there in the circuit, it may blow off and break the circuit, thus preventing damage to electric circuits and possible fires. Thus, electric fuses are called safety devices.
Question 2.
What is electromagnet? Write various uses of the electromagnet.
Answer:
A core of magnetic material surrounded by a coil of wire behaves like a magnet when electric current flows through it. When the electric current is switched off, the coil generally losses its magnetism. Such coils are called electromagnet.
Various uses of the electromagnet are as follows:
- It is used in separating magnetic materials such as iron, nickel, and cobalt from the garbage heaps.
- It is used in making appliances such as electric bells, telephones, audio players, and recorders.
- It is used in taking out tiny pieces of magnetic material that have accidentally fallen in the eye.
- It is used in various toys.
- Bullet trains use the principle of electromagnetism.
- Audio and video tapes use the principle of electromagnetism.
Question 3.
What are the differences between electromagnet and permanent magnet?
Answer:
The differences between electromagnet and a permanent magnet are as follows :
| S.No. | Electromagnet | Permanent magnet |
| 1) | It is usually made up of soft materials. | It is usually made up of hard materials. |
| 2) | Removal of magnetic properties is temporary. | Once magnetic properties are lost, it becomes useless. |
| 3) | The magnetic properties that are displayed when current is passed through it. | Magnetic properties exist even when no current is there. |
| 4) | The poles of this kind of magnet can be altered with the flow of current. | The poles of this kind of magnet cannot be changed and are fixed. |
| 5) | The strength is adjusted depending upon the amount of flow of current. | The strength depends upon the nature of the material used in its creation. |
Question 4.
Draw the symbols of the following circuit components.
a) electric cell
b) switch in OFF position
c) electric bulb
d) battery
Answer:
Question 5.
When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.
Answer:
We know that the needle of a compass is a tiny magnet, which points in north-south direction. When we bring a magnet close to it, the needle gets deflected. Also, when an electric current flows through a wire, it produces magnetic effect around it. Therefore, when the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position due to magnetic effect of electric current around the wire.
Question 6.
Write short notes on short circuiting and overloading.
Answer:
Short circuiting : Short-circuiting occurs in a circuit when the live wire comes in direct contact with the neutral wire. This causes much damage to the electric appliances connected with them.
Overloading: Overloading occurs in a circuit when the current in the circuit increases abruptly. It causes overheating of the wire and might lead to the fire. It can also occur due to accidental increase in the supply voltage or on connecting too many appliances to a single socket.
Question 7.
Explain the working of an electric bell.
Answer:
An electric bell consists of a coil of wire wrapped in an iron piece. It is connected to the source of current through a switch. It has a metallic gong, a hammer to strike the gong, and a contact screw attached to the iron strip. When the iron strip is in contact with the screw, the current flows through the coil which becomes an electromagnet.
It pulls the iron strip, in this process the hammer at the end of the strip strikes the gong of the bell to produce a sound. But when the electromagnet, pull the iron strip, it also breaks the circuit. The current through the coil stops flowing. The iron strip comes back to its original position and touches the contact screw. This completes the. circuit again and the process is repeated in quick succession and the bell rings
Case Based / Data – Based Questions.
Mohan saw her mother running microwave, oven, electric rice cooker, and mixer grinder from a single socket. He immediately rushed to his mother and remind her of overloading and its consequences. Mohan’s mother immediately turned off the switch and connected them one by one according to her needs. She felt very happy for Mohan for his presence of mind.
i) What is overloading?
Answer:
It can occur due to accidental increase in the supply voltage or on connecting too many appliances to a single socket.
(Or)
When excess amount of electric current passes through excessive heating takes place, this is called overloading.
ii) What is the full form of MCB?
Answer:
The full form of MCB is “Miniature Circuit Breakers”
iii) What are the consequences of overloading?
Answer:
The consequences are overloading it can damage the Circuit of house. It can also leads to fire.
iv) What role do MCB plays in case of overloading?
Answer:
When there is overloading of current, MCB trips and switches off, which in turn cut off the supply of electricity, and thus protect us from damages due to overloading of current.