GSEB Class 7 Science Solutions Chapter 14 Electric Current and its Effects

 

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:

In simple words: These drawings show the basic signs for parts used in electric circuits, helping us understand how they are connected without seeing the actual items.

Exam Tip: Remember to clearly distinguish between the 'on' and 'off' switch positions and the symbols for a single cell versus a battery (multiple cells).

 

Question 2. Draw the circuit diagram to represent the circuit shown in fig.
Answer:

This represents a simple circuit with a bulb and a single cell. The cell provides electrical energy, and the bulb lights up when the circuit is complete.
In simple words: The picture shows a circuit. We draw a diagram using special symbols: one for the light bulb and one for the power cell, connected with lines for wires.

Exam Tip: Always use standard circuit symbols. Ensure the connections are clearly drawn to show a closed loop for current to flow.

 

Question 3. This Figure shows four cells fixed on aboard. Draw lines to indicate how you will connect their terminals with wires to make a battery of four cells.
Answer: To create a battery from multiple cells, you must connect the positive terminal of one cell to the negative terminal of the next cell. This series connection ensures that the total voltage increases, allowing the cells to work together effectively as a single power source. The final connection will have the first cell's negative terminal and the last cell's positive terminal available for external circuit connections.
In simple words: To make a battery with these cells, link the plus end of one cell to the minus end of the next cell. Keep doing this until all four cells are joined up. This way, they work together as one bigger power source.

Exam Tip: Remember the rule for connecting cells in series: positive to negative. This arrangement increases the total voltage of the battery.

 

Question 4. The bulb in the circuit shown in fig. does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.
Answer: The main issue in this circuit is how the two cells are joined. To make the bulb light up, the positive terminal of one cell must be connected to the negative terminal of the other cell. If they are connected positive-to-positive or negative-to-negative, the circuit will not function correctly, and the bulb will not glow. The connections need to be changed to ensure a proper series arrangement for the current to flow.
In simple words: The problem is how the two power cells are linked. To make the light bulb work, you need to connect the plus side of one cell to the minus side of the other.

Exam Tip: When connecting cells, always check for the correct polarity (positive to negative in series) to ensure the circuit works as intended.

 

Question 5. Name any two effects of electric current.
Answer: Electric current can have several noticeable effects. Two common effects are:

• Electric current can lead to heating and illumination.
• Electric current can change a straight conductor into a temporary magnet.

In simple words: Electricity can make things hot and glow, like in a light bulb. It can also turn a simple wire into a temporary magnet.

Exam Tip: Be ready to explain these effects with simple examples, such as a toaster (heating) or an electromagnet (magnetic effect).

 

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: When electric current flows through a wire, it causes the compass close to it to move from its normal north-south direction, much like a magnet would. This phenomenon is called the magnetic effect of electric current. Since a compass needle is actually a small, thin magnet itself, when it comes near another magnet (the current-carrying wire), the opposite poles pull each other, and similar poles push each other away. This interaction causes the needle to shift or deflect, as the wire temporarily acts like a magnet, influencing the compass.
In simple words: When electricity flows through a wire, it makes the wire act like a magnet. Because a compass has a tiny magnet inside, it moves when it's near another magnet (the wire), showing the magnetic effect of electric current.

Exam Tip: This question describes Oersted's experiment. Mentioning the magnetic effect of current is key to scoring full marks.

 

Question 7. Will the compass needle show deflection when the switch in the circuit shown by fig. is closed?
Answer: No, the compass needle will not show any deflection. This is because there is no source of electric current present in this specific circuit, meaning there is no battery or cell to provide power. For an electric current to flow and create a magnetic field that would cause the compass to move, a power source is absolutely necessary.
In simple words: No, the compass will not move. There is no power source like a battery in the circuit, so no electricity flows to make a magnetic field.

Exam Tip: A closed circuit only conducts current if a power source (like a battery or cell) is included. Without it, no magnetic effect will be observed.

 

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.
In simple words: The long line on a cell symbol means the positive end. Many cells together make a battery. A heater gets hot and glows when switched on. A fuse is a safety item that uses heat to break the circuit.

Exam Tip: Knowing standard circuit symbols and the basic effects of electric current is crucial for these types of questions.

 

Question 9. Mark 'T' if the statement is true and 'F' if 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 electromagnet. (T/F)
Answer:
(a) False
(b) True
(c) False
(d) True
In simple words: To make a battery, connect the negative end of one cell to the positive end of another. Fuses melt if too much current flows. Electromagnets do attract iron. Electric bells use electromagnets to work.

Exam Tip: Understand the correct way to connect cells, the function of a fuse, and the basic properties and applications of electromagnets.

 

Question 10. Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.
Answer: No, an electromagnet cannot be used to separate plastic bags from a pile of garbage. The reason is that plastic bags are not attracted by magnets. Electromagnets only attract materials that are magnetic, such as iron or steel. Since plastic does not possess magnetic properties, it would simply remain unaffected by the electromagnet, making it useless for this particular separation task.
In simple words: No, an electromagnet cannot sort out plastic bags from trash. Magnets only pull in magnetic things like iron, and plastic is not magnetic.

Exam Tip: Remember that electromagnets (and all magnets) only attract ferromagnetic materials; they cannot be used to separate non-magnetic items like plastic.

 

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, you should not agree to allow the electrician to replace a fuse with just any piece of wire. Fuses are designed with wires that have very specific melting points, which are carefully chosen to break the circuit when too much current flows, protecting appliances and preventing hazards like short circuits or fires. Using an ordinary piece of wire could be dangerous because it might not melt at the correct current level, potentially causing significant damage or safety risks. Therefore, it is important to always use ISI-marked fuses that meet safety standards in electrical systems.
In simple words: No, don't let the electrician use a regular wire for a fuse. Real fuses have special wires that melt at a certain heat to keep your house safe from electrical problems. Using a normal wire is dangerous.

Exam Tip: Emphasize the safety aspect of fuses and the dangers of using incorrect substitutes. Mentioning ISI marks adds credibility to your answer.

 

Question 12. Zubeda made an electric circuit using a cell holder shown in given fig. 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: For Zubeda's bulb to glow, she needs to check several potential issues in her circuit:

1. **Cell Connection:** It is crucial that the cells are placed in the correct series orientation. The positive terminal of the first cell must connect to the negative terminal of the second cell, and so on. Incorrect connections will prevent current flow.
2. **Switch Position:** The switch must be fully closed and in the 'ON' position to complete the circuit. A loose or partially closed switch will interrupt the flow.
3. **Bulb Condition:** The bulb itself might be fused (burnt out). She should check if the filament inside the bulb is intact.
4. **Loose Wires:** All wire connections should be firm and secure. Loose connections can break the circuit.

If Zubeda examines and corrects these points, her bulb will almost certainly light up.
In simple words: Zubeda should check if the power cells are connected correctly (plus to minus). She also needs to make sure the switch is fully 'on' and that the light bulb itself is not broken. All the wires must be connected tightly.

Exam Tip: When troubleshooting a non-working circuit, systematically check all components: power source, connections, switch, and load (bulb) in a logical order.

 

Question 13. In the circuit shown in fig.
1. Would any of the bulb glow when the switch is in the 'OFF' position?
2. 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:
1. No bulb will glow when the switch is in the 'OFF' position. This is because an 'OFF' switch creates an open circuit, preventing the flow of electricity to any of the bulbs.
2. All bulbs (A, B, and C) will glow simultaneously when the switch is moved to the 'ON' position. In a series circuit, current reaches all components at the same instant, causing them to light up at the same time.
In simple words: If the switch is 'off', no light bulbs will work because the circuit is broken. When the switch is 'on', all the light bulbs (A, B, and C) will light up at the exact same moment.

Exam Tip: Understand that an open switch prevents current flow in the entire circuit. In a series circuit, current flows through all components at once.

Extended Learning Activities And Projects

 

Question 1. Set up the circuit shown above in Fig. of NCERT again. Move the key to 'ON' position and watch carefully in which direction the compass needle gets deflected. Switch 'OFF' the current. Now keeping the 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 explanation.
Answer: When the key is moved to the 'ON' position, the compass needle is observed to deflect in a specific direction. When the current is switched 'OFF', the needle returns to its original position. Furthermore, if the direction of the current is reversed by changing the cell's connections, the compass needle's deflection direction also changes.
This activity clearly demonstrates two important principles:

• Electricity produces a magnetic effect.
• If the direction of the electric current is altered, then the direction of the magnetic field it creates also changes.

In simple words: When you turn the electricity on, a compass needle nearby moves. When you turn it off, the compass goes back. If you flip the battery connections, the compass moves in the opposite direction. This shows electricity makes magnetism, and changing the power direction also changes the magnetism direction.

Exam Tip: This experiment is crucial for understanding the relationship between electricity and magnetism. Key points are deflection with current, return to original position without current, and reversal of deflection with reversal of current direction.

 

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: Students will observe that the electromagnet with 80 turns will attract the largest number of pins, indicating it has the greatest strength. As the number of turns in the coil increases, the strength of the electromagnet also increases. This activity effectively demonstrates that the strength of an electromagnet is directly proportional to the number of turns in its coil. The general rule is:
Strength of magnet \( \propto \) Number of turns
In simple words: If you make magnets with different amounts of wire turns, the one with 80 turns will be the strongest, picking up the most pins. This experiment shows that more wire turns mean a stronger electromagnet.

Exam Tip: The key takeaway is the direct relationship between the number of turns in the coil and the strength of the electromagnet. Always state this relationship clearly.

 

Question 3. Using an electromagnet, you can make a working model of a railway signal as shown in Fig.
Answer: To create a working model of a railway signal using an electromagnet, you would typically need a base, an iron core (like a large nail or bolt), insulated copper wire to coil around the core, a power source (battery), and a pivotable signal arm made of a magnetic material or with a magnetic piece attached.
When current flows through the coil, the iron core becomes magnetized, attracting the signal arm and causing it to move to one position (e.g., 'stop'). When the current is switched off, the electromagnet loses its magnetism, and the arm springs back to its original position (e.g., 'go'). This action mimics how real railway signals operate using electromagnetic principles. This is a practical activity that helps students grasp how electromagnets are employed in everyday technology.
In simple words: To make a model railway signal, use an electromagnet to move a signal arm. When electricity turns the magnet on, it pulls the arm to show 'stop'. When the electricity is off, the magnet loses its power, and the arm moves back to 'go'. This shows how magnets help run real signals.

Exam Tip: When describing a model, clearly state the main components (electromagnet, signal arm, power source) and explain the mechanism of attraction and release based on the electromagnet's activation and deactivation.

 

Question 4. Visit an electric shop. Request a mechanic to show you the various types of fuses and MCB and to explain how they work.
Answer: Fuses and Miniature Circuit Breakers (MCBs) both operate based on the heating effect of electric current, acting as safety devices in electrical circuits. They are designed to trip or break the circuit when the current flowing through them surpasses a predetermined safe limit. If the electrical current increases beyond this specified level, the fuse wire will melt and break the circuit, or the MCB will automatically trip, cutting off the power supply. This action prevents potential damage to appliances, wiring, and minimizes the risk of electrical fires, thereby protecting the entire electrical system.
In simple words: Fuses and MCBs both protect electrical circuits by using heat. When too much electricity flows, the fuse melts or the MCB switches off the power. This stops damage and keeps things safe.

Exam Tip: Focus on the common principle (heating effect of current) and the safety function (breaking the circuit) for both fuses and MCBs.