A. Choose the correct option
1. Which of these is a basic component of an electric circuit?
a. An electric toaster
b. An electric bell
c. A source of electric current
d. An electromagnet
Answer: c. A source of electric current
2. Which of the following appliances function because of the heating effect of current?
a. Electric fan
b. Washing machine
c. Toaster
d. Mixer grinder
Answer: c. Toaster
3. Which of the following acts as a safety device to prevent a large amount of electric current from flowing through a circuit?
a. Electric cell
b. Electric fuse
c. Electric bulb
d. Conducting wires
Answer: b. Electric fuse
4. Which of the following is not a component of an electromagnet?
a. Soft iron core
b. A source of current
c. A light bulb
d. An insulated current-carrying wire
Answer: c. A light bulb
B. Fill in the blanks with the correct words
- The standard method for drawing electric circuits is called circuit diagrams.
- A fuse is a safety device that limits the amount of current in an electric circuit.
- An electromagnet acts like a magnet only when an electric current is on.
- Electric iron is based on the heating effect of electric current.
- An electric bell is based on the magnetic effect of electric current.
C. Give reasons for the following
1. It is important to have standard methods of drawing circuit diagrams.
Answer: Standard circuit symbols make diagrams easy to understand for everyone, no matter where they are from. It helps scientists, engineers, and students communicate clearly and correctly.
2. Sometimes filaments in an electric bulb get fused.
Answer: The filament in a bulb gets fused when too much current flows through it, causing it to overheat and break.
3. Electric fuse wire is made of a material with a low melting point.
Answer: The fuse wire melts quickly when extra current flows through the circuit. This breaks the circuit and prevents damage to electrical appliances.
5.A metal safety pin stuck to an electromagnet falls down when the current in the electromagnet is switched off.
Answer: When the current is switched off, the electromagnet loses its magnetic power, so the metal pin is no longer attracted and falls down.
D. Answer the following questions
a. Define/Explain the following terms
i. Electric circuit
Answer: An electric circuit is a closed path in which electric current flows from the source through wires and devices and back to the source.
ii. Electric circuit diagram
iii. Heating element
Answer: A heating element is a part of an appliance that converts electrical energy into heat, such as the coil in an iron or toaster.
iv. Electric fuse
Answer: An electric fuse is a safety device that protects circuits by melting and breaking the flow of current when too much current passes through it.
v. Electromagnet
Answer: An electromagnet is a temporary magnet made by passing electric current through a coil of wire wound around a soft iron core. It becomes magnetic only when the current flows.
2. What is heating effect of electric current?
Answer:
The heating effect of electric current is the phenomenon where electrical energy is converted into heat energy when current flows through a conductor. This happens because the electrons moving through the conductor collide with its atoms and ions, transferring their kinetic energy. This energy manifests as heat, raising the temperature of the conductor.
3. Name two appliances that use heating effect of electric current.
Answer:
Two common appliances that utilize the heating effect of electric current are:
- Electric Iron
- Electric Heater
(Other examples: Toaster, Electric Kettle, Room Heater)
4. What is an electric fuse, and how is it useful?
Answer:
An electric fuse is a safety device that protects electrical circuits from excessive current. It consists of a short piece of metal wire that has a low melting point and a specific current rating.
It is useful because when the current in a circuit accidentally exceeds a safe value (due to a short circuit or overloading), the heat generated melts the fuse wire. This breaks the circuit and stops the flow of current, thereby preventing damage to appliances and potential fire hazards.
5. What is an electromagnet? What are its properties?
Answer:
An electromagnet is a temporary magnet that is created when an electric current flows through a coil of insulated wire wound around a soft iron core. Its magnetic effect disappears as soon as the current is switched off.
Properties of an Electromagnet:
- Its magnetic strength can be changed by varying the electric current or the number of turns in the coil.
- Its polarity (North and South poles) can be reversed by reversing the direction of the electric current.
- It is a temporary magnet; it loses its magnetism once the current is stopped.
- It is generally much stronger than a permanent magnet of a similar size.
6. Give two uses of electromagnets.
Answer:
Two important uses of electromagnets are:
- In Electric Bells: Used to create a repetitive sound by attracting a soft-iron armature attached to a hammer.
- In Cranes: Used in scrap yards to lift and move heavy loads of magnetic material like iron and steel.
7. In an electric bell, explain the function of the following parts
a. Switch
Answer: The switch is used to complete or break the electric circuit. When pressed, it allows current to flow through the circuit, activating the bell. When released, it stops the current, turning the bell off.
- Electromagnet
Answer: The electromagnet gets magnetized when current flows through its coil. This magnetism attracts the nearby soft-iron strip (armature), causing the hammer to strike the gong.
c. Soft-iron strip
Answer: The soft-iron strip, also called the armature, is attached to a springy metal strip. It is attracted towards the electromagnet when it becomes magnetized. This movement causes the hammer to hit the gong.
d. Hammer and gong
Answer: The hammer is a metal piece attached to the soft-iron strip. When the strip moves, the hammer strikes the gong (a metal cup), producing a ringing sound.
8. How will you show that a current carrying wire produces a magnetic field?
Answer:
This can be demonstrated through a simple activity:
- Take a straight, thick copper wire and place it in the North-South direction between the points of a magnetic compass.
- Ensure the wire is connected to a battery and a switch to form a complete circuit.
- Observe that the compass needle is parallel to the wire when no current is flowing.
- Now, pass a strong electric current through the wire.
- You will observe that the compass needle deflects from its original position.
- If the current is reversed, the needle will deflect in the opposite direction.
This deflection proves that a magnetic field is produced around the current-carrying wire, which exerts a force on the compass needle.