GSEB Class 7 Science Solutions Chapter 14 વિધુતપ્રવાહ અને તેની અસરો

Textbook Exercise Questions and Answers

Question 1. Draw symbols representing the electrical components of an electric circuit in your notebook: connecting wire, 'OFF' position switch, electric bulb, electric cell (Cell), 'ON' position switch, and battery.
Answer: The electrical symbols are represented as follows:
Connecting wire: —
Switch in 'OFF' position: —o / o—
Electric bulb: —\(\otimes\)—
Electric cell (Cell): —\(\textbf{+| |-}\)—
Switch in 'ON' position: —o—o—
Battery: —\(\textbf{+| |-|}\)\(\textbf{|-}\)—
In simple words: Each part of an electric circuit has a special drawing symbol. These symbols help us to quickly understand how a circuit is put together without drawing actual pictures.

Exam Tip: Memorize the standard circuit symbols as they are essential for drawing and interpreting circuit diagrams accurately.

Question 2. Draw the circuit diagram representing the electrical circuit shown in the figure.
Answer: The circuit diagram for the given electrical circuit is as follows: The positive terminal of an electric cell is linked to one end of a switch. The negative terminal of the cell is linked to one terminal of the electric bulb. The other terminal of the switch is linked to the remaining terminal of the bulb, forming a closed circuit.
In simple words: Imagine a battery, a switch, and a light bulb. Connect them all in a loop using wires, so electricity can flow from the battery, through the switch, to the bulb, and back to the battery. That's the simple drawing.

Exam Tip: Always ensure the circuit forms a complete loop for current to flow and the bulb to glow.

Question 3. Four cells are arranged on a wooden board in the figure. Draw a diagram showing how you would connect their terminals with a wire to form a battery of four cells.
Answer: To form a battery with four cells, you must connect the positive terminal of one cell to the negative terminal of the following cell. This connection pattern is continued for all cells, so the final arrangement has the positive terminal of the first cell and the negative terminal of the last cell available for use.
In simple words: To make a battery from many small cells, you hook up the plus side of one cell to the minus side of the next cell, and keep doing this in a line.

Exam Tip: Correctly connecting positive and negative terminals in series is crucial for the battery to function and provide the intended voltage.

Question 4. The bulb in the electric circuit shown in the figure is not glowing. Can you identify this problem? Make necessary changes in the electric circuit for the bulb to glow.
Answer: The main issue is with how the two electric cells are linked. In the given diagram, both positive terminals are connected together, which prevents the flow of current. The problem can be fixed by connecting the positive terminal of one cell to the negative terminal of the other cell. Once this correction is made, the bulb will glow brightly. The circuit needs to be joined correctly for it to work properly.
In simple words: The cells are connected the wrong way, with plus sides together. Change it so a plus side connects to a minus side, and the light bulb will turn on.

Exam Tip: Always check cell polarity (+ to -) when connecting batteries in a circuit to ensure proper current flow.

Question 5. Name two different effects of electric current.
Answer: The two distinct effects of electric current are as follows:
1. The heating effect of electric current.
2. The magnetic effect of electric current.
In simple words: When electricity flows, it can either make things hot or create a magnetic field around them.

Exam Tip: Remember these two fundamental effects, as many electrical devices rely on one or both principles.

Question 6. When current is switched on in a wire, the compass needle nearby deflects from its north-south direction. Explain.
Answer: A compass needle is essentially a tiny magnet that naturally points in the north-south direction. When an electric current flows through a wire, that wire begins to act like a magnet. This action produces a magnetic field around the wire. Just as a compass needle moves when a regular magnet comes close to it, the compass needle near the current-carrying wire also deflects. This happens because the magnetic influence of the wire makes the compass needle shift from its usual north-south resting position.
In simple words: A compass needle is a small magnet. When electricity runs through a nearby wire, the wire becomes a temporary magnet and pushes the compass needle, making it move from its normal north-south pointing.

Exam Tip: This phenomenon, known as Oersted's discovery, demonstrates the direct link between electricity and magnetism.

Question 7. Will the compass needle show deflection when the circuit in the figure is completed by the switch?
Answer: No, the compass needle will not show any deflection. This is because there is no power source, such as an electric cell, connected in the circuit shown. Without a power source, electric current cannot flow through the circuit at all. Consequently, there will be no magnetic field generated around the wire to cause the compass needle to move.
In simple words: No, the compass won't move. There's no battery in the circuit, so no electricity will flow to make the wire magnetic.

Exam Tip: A complete circuit requires a power source, connecting wires, and a load (or device) to allow current to flow and produce effects like magnetism.

Fill in the Blanks:

Question 1. In the symbol of an electric cell, the long line represents the .................. terminal.
Answer: Positive
In simple words: The longer line in the cell symbol shows the positive end.

Exam Tip: Always remember that the longer line in a cell symbol signifies the positive terminal, while the shorter line represents the negative terminal.

Question 2. A combination of two or more electric cells is called a .................. .
Answer: Battery
In simple words: When you put two or more cells together, it's called a battery.

Exam Tip: Batteries provide a higher voltage than single cells, making them suitable for devices requiring more power.

Question 3. When electric current is switched on in a room heater, it .................
Answer: Produces heat
In simple words: A room heater gets hot when electricity flows through it.

Exam Tip: This is an example of the heating effect of electric current, where electrical energy is converted into thermal energy.

Question 4. A safety device used based on the heating effect of electric current is called a .................. .
Answer: Fuse
In simple words: A fuse is a safety item that uses heat from electricity to protect other things.

Exam Tip: Fuses are crucial for safety, as they break the circuit when current exceeds a safe limit, preventing damage to appliances and fires.

Mark 'T' for True Statements and 'F' for False Statements:

Question 1. To make a battery of two electric cells, one electric cell's three terminals are connected to the negative terminal of the other electric cell.
Answer: F
In simple words: This statement is false because an electric cell only has two terminals, not three, and to make a battery, the positive of one cell connects to the negative of the next.

Exam Tip: Cells have only two terminals (positive and negative); ensure correct polarity connections to form a functional battery.

Question 2. When the electric current flowing through a fuse exceeds its limit, the fuse wire melts and breaks.
Answer: T
In simple words: If too much electricity goes through a fuse, its special wire gets hot, melts, and breaks the circuit, stopping the power.

Exam Tip: Fuses are designed with specific melting points to protect circuits from overcurrents, acting as safety devices.

Question 3. An electromagnet does not attract pieces of iron.
Answer: F
In simple words: This statement is false because electromagnets are designed specifically to attract iron pieces when electricity runs through them.

Exam Tip: Electromagnets are temporary magnets that attract magnetic materials like iron only when current flows through them.

Question 4. An electromagnet is present in an electric bell.
Answer: T
In simple words: An electric bell has an electromagnet inside it that helps make the ringing sound.

Exam Tip: Electric bells utilize the magnetic effect of electric current, where an electromagnet pulls a hammer to strike a gong.

Question 10. Do you think an electromagnet can be used to separate plastic bags from a garbage heap? Explain.
Answer: No, an electromagnet cannot be used to separate plastic bags from a pile of waste. This is because electromagnets, or any magnet for that matter, are designed only to attract magnetic materials, such as iron. Plastic, however, is not a magnetic substance. Consequently, an electromagnet would not be able to pull or separate plastic bags from the garbage. Hence, it is not a viable tool for this purpose.
In simple words: No, you can't use an electromagnet for plastic bags. Electromagnets only pick up things made of iron, and plastic is not magnetic.

Exam Tip: Remember that electromagnets are effective for separating metallic waste (containing iron or other magnetic materials) but not non-magnetic materials like plastic.

Question 11. After doing some repair work in your house, an electrician wants to use a piece of wire to replace the fuse. Do you agree with this? State the reason for your response.
Answer: No, I would not agree with the electrician's decision to use an ordinary piece of wire to replace the fuse. Fuses are vital safety devices, and only specific, ISI-marked fuse wire should be employed. It is highly improper for an electrician to use any random piece of wire. Using an incorrect wire as a fuse can result in severe damage to electrical appliances, increase the risk of electrical fires, and pose a significant danger to the household.
In simple words: No, this is a bad idea. Fuses need special wire to keep your house safe from fire and damage. Using a regular wire can be very dangerous.

Exam Tip: Always insist on the use of appropriate, certified fuse wire for replacements to ensure electrical safety.

Question 12. As per the figure below, Zubeda made an electric circuit using a cell holder. When she switches 'ON' the circuit, the bulb does not glow. Help Zubeda identify the possible faults in the circuit.
Answer: Zubeda's circuit might have the following possible faults:
(1) Zubeda may not have connected the two electric cells correctly. She might have connected the positive terminal of one cell to the positive terminal of the other, instead of connecting positive to negative.
(2) The electric bulb she used might be faulty or burnt out.
In simple words: The problem could be that the batteries are hooked up wrong (plus to plus instead of plus to minus), or the light bulb itself is broken.

Exam Tip: When troubleshooting circuits, always check the power source connection and the functionality of the load (like a bulb) first.

Question 13. (i) When the switch is in the 'OFF' position, will any bulb glow?
Answer: When the switch is in the 'OFF' position, none of the bulbs will glow. This happens because, in the 'OFF' state, the electric current cannot flow through the circuit. As a result, no bulb will receive power and light up.
In simple words: No, if the switch is off, no electricity can flow, so the light bulbs won't turn on.

Exam Tip: An open switch (OFF position) breaks the continuity of the circuit, preventing current flow.

Question 13. (ii) When the switch is moved to the 'ON' position in the circuit, in what order will bulbs A, B, and C glow?
Answer: When the switch is moved to the 'ON' position in the circuit, electric current starts flowing instantly through the entire circuit. Therefore, all three bulbs — A, B, and C — will glow simultaneously, without any specific order or delay between them.
In simple words: When the switch is turned on, electricity goes everywhere at once, so all the light bulbs (A, B, and C) will light up at the same time.

Exam Tip: In a simple series or parallel circuit, current flows to all components nearly instantaneously, causing them to operate concurrently.

GSEB Class 7 Science Electric Current and Its Effects Textbook Activities

Understanding Textbook Activities

Activity 1:

Drawing the Electric Circuit Diagram.

Procedure:

1. Draw this electric circuit in your notebook.

2. Draw its electric circuit diagram using symbols for various electrical components. Does your diagram align with the circuit diagram presented below?

Activity 2:

Observing the Heating Effect of Electric Current.

Materials Required: electric cell, electric bulb, electric switch, connecting wires.

Procedure:

1. Take an electric cell, an electric bulb, an electric switch, and connecting wires.

2. Prepare the electric circuit as illustrated in the adjacent figure.

3. Keep the electric switch in the open (OFF) position. Does the bulb glow? Touch the bulb.

4. Now bring the electric switch to the ON position and let the electric bulb glow for approximately 1 minute.

5. Touch the bulb again. Do you notice any change?

6. Bring the electric switch back to the open (OFF) position and touch the bulb again.

Observation:

1. When the electric switch is in the OFF position, the bulb does not become warm.

2. When the electric switch is in the ON position, the bulb becomes warm.

3. After returning the electric switch to the OFF position, touching the bulb after a short while shows it has cooled down.

Conclusion:

When electric current flows through the electric bulb, the bulb becomes hot. This phenomenon occurs due to the heating effect of electric current.

Activity 3:

Observing the Heating Effect of Electric Current Using Nichrome Wire.

Materials Required: A piece of nichrome metal wire, electric cell, electric switch, two nails, a thermocol piece.

Procedure:

1. Prepare the electric circuit as displayed in the figure.

2. Take a piece of nichrome metal wire, around 10 cm long, and tie it between two nails on a thermocol sheet. Position the nails on the thermocol sheet. Touch the wire.

3. Now, move the electric switch to the ON position and allow electric current to flow in the circuit. After a few seconds, touch the wire once more. (Avoid keeping your hand on the wire for an extended period.)

4. Bring the electric switch to the OFF position to halt the current flow. After some minutes, touch the wire again.

Observation:

When electric current flows through the wire, it becomes warm.

Conclusion:

When electric current passes through it, the nichrome wire gets hot. This demonstrates the heating effect of electric current.

Activity 4:

Demonstrating the Functioning of an Electric Fuse.

Procedure:

1. Recreate the electric circuit that was used for Activity 3.

2. Replace the single electric cell with a battery containing 4 electric cells. Also, substitute the nichrome wire with a thin strand of steel wool. (Steel wool is typically used for cleaning utensils and can be found at grocery stores.)

3. Now, permit electric current to flow through the circuit for a brief period.

4. Carefully observe the strand of steel wool. Did the steel wool strand melt or break apart?

Observation:

When electric current passes through the circuit, the steel wool strand melts and breaks.

Conclusion:

When a substantial electric current flows through specific types of metal wires, these wires rapidly melt and break. Such wires are commonly used to create 'electric fuses'.

Activity 5:

Proving that a Wire Behaves as a Magnet When Electric Current Passes Through It.

Materials Required: Matchbox, electric wire, electric cell, electric bulb, electric switch, compass needle.

Procedure:

1. Take out the inner tray from an empty matchbox. Then, wrap an electric wire several times around it.

2. Place a small compass inside the tray.

3. Next, connect both ends of the wire to an electric switch and an electric cell, as illustrated in the figure.

4. Note down the direction in which the compass needle comes to rest.

5. Bring a bar magnet close to the compass needle and observe what occurs.

6. Now, while carefully watching the compass needle, move the electric switch to the 'ON' position. What did you notice? Did the compass needle show any deflection?

7. Move the electric switch to the 'OFF' position. Did the compass needle return to its original position? Repeat the experiment a few times. What does this experiment illustrate?

Observation:

1. When a bar magnet is brought close to the compass needle, the needle deflects.

2. When electric current flows through the circuit, the compass needle shows deflection.

3. When the electric switch in the circuit is turned OFF, stopping the electric current, the compass needle returns to its original north-south position.

Conclusion:

When electric current flows through the electric wire in a circuit, the nearby compass needle deflects. This shows that the electric wire acts like a magnet during this period.

Activity 6:

Making an Electromagnet from a Given Iron Nail.

Materials Required: Iron nail, insulated wire, electric cell, electric switch.

Procedure:

1. Obtain an insulated (plastic or cloth-covered) bendable wire, approximately 75 cm long, and an iron nail measuring 6 to 10 cm in length.

2. Tightly wrap the wire around the nail, forming a coil.

3. Connect both free ends of the wire to an electric cell and an electric switch, as depicted in the figure.

4. Place a few pins near or directly on the nail.

5. Now, activate the electric current. What occurs? Do the pins adhere to the tip of the nail?

6. Deactivate the electric current. Are the pins still attached to the tip of the nail?

Observation:

The coil of wire behaves like a magnet when electric current flows through it. When the electric current is turned off, the coil of wire loses its magnetic properties.

Conclusion:

By allowing electric current to pass through it, an iron nail is transformed into an electromagnet.