EXERCISE-9A
Question 1. At what voltage and frequency is the electric power generated at the power generating station?
Solution:
At the power generating facility, electric power is produced at 11 KV, 50Hz.
Question 2. (i) At what voltage is the electric power from the generating station transmitted? Give reason to your answer.
(ii) What is the nature of current transmitted from the power station?
Solution:
(i) Because voltages above this cause insulation issues and voltages below this result in significant current and energy loss as heat (I2 RT), electrical power from producing stations is transported at 11 kV.
(ii) Alternating current is what is transmitted from the power plant.
Question 3. The voltage of power generated at the generating stations is first stepped up before its transmission. Give reason.
Solution:
Typically, producing plants produce power at a very high voltage of roughly 11kV.
The transmission of this power from the producing plants across great distances is required.
A significant amount of energy is wasted in the transmission line wires as heat when delivering the 11 kV electricity
As a result, the step-up transformer raises or steps up the voltage of the power produced at the stations from 11 kV to 132 kV.
This procedure can only be used with alternating current because direct current cannot be increased.
Question 4. Explain with the aid of a simple diagram, the transmission of electric power from the generating station to your house.
Solution:
Electricity is produced by a power plant with a voltage of 11 kV. A step-up transformer is then used to transport the alternating voltage to the grid sub-station and step it up to 132 kV from there. The voltage is then stepped down to 33 kV using a step-down transformer at the main sub-station before being transferred to the intermediate sub-station. The power is first stepped down to 11 kV at the intermediate sub-station and then sent to the city sub-station, where it is further stepped down to 220V and provided to our homes.
Question 5. At what voltage and frequency is the a.c. supplied to our houses?
Solution:
Our homes receive ac power at a frequency of 50 Hz and a voltage of 220 V.
Question 6. Name the device used to (a) increase the voltage at the generating station (b) decrease the voltage at the substation for its supply.
Solution:
(a) Step-up transformers
(b) Step-down transformers
Question 7. (a) Name the three connecting wires used in a household circuit
(b) Which of the two wires mentioned in part (a) are at the same potential?
(c) In which of the wire stated in part (a) the switch is connected?
Solution:
(a) A domestic circuit consists of three connecting wires: an earth wire, a neutral wire, and a live (or phase) wire (E).
(b) The potential of the neutral and earth cables among them is the same.
(c) A live wire is attached to the switch.
Question 8. What is the pole fuse? Write down its current rating.
Solution:
A fuse with a rating of (50 A) is inserted in the live wire at the pole or immediately before the metre before the electric line is connected to the metre in a home. The pole fuse is the name of this fuse. It now has a grade of 50 A.
Question 9. State the function of the following in a house circuiting
(i) kWh meter
(ii) Main fuse
(iii) Main switch
Solution:
(i) The cable is linked to a kWh metre after the company fuse, and connections are made to the distribution board through a main fuse and a main switch from this metre.
(ii) The main fuse is attached to the live wire, and if a strong current flows through it, it burns, cutting the connections and protecting the appliances.
(iii) The live and neutral wires are linked to the main switch. It is used to simultaneously disconnect the connections to the live and neutral wires coming from the main supply.
Question 10. In what unit does the electric meter in a house measure the electrical energy consumed? What is its value in S.I. unit?
Solution:
Kilowatt-hours are used by the household electric metre to monitor electrical usage (kWh).
1 kWh = 1 kilowatt × 1 hour
= 1000 Js-1 × (60 × 60) s
= 3.6 × 106 J in S.I. unit.
Question 11. Where is the main fuse in a house circuit connected?
Solution:
On the distribution board, on the live wire ahead of the main switch, is where the primary fuse for a house circuit is attached.
Question 12. State one advantage of using the main switch in house wiring
Solution:
A twin pole switch with an iron covering serves as the main switch. The key benefit of employing a main switch is that it may simultaneously cut the connection between the live and neutral wires. This shields electrical equipment against unintentional damage brought on by electrical problems.
Question 13. Draw a circuit diagram to explain the ring system of house wiring. State two advantage of it
Solution:
Advantages of ring system over tree system:-
(i) Wiring in a ring system is less expensive than in a tree system.
(ii) In a tree system, sockets and plugs are of various sizes, but in a ring system, sockets and plugs of the same size can be utilized.
(iii) In a tree system, when a fuse in one distribution line blows, it disconnects all the appliances connected to that distribution circuit. In a ring system, however, each appliance has a separate fuse, so if there is a fault and the fuse of one appliance burns, it does not affect other appliances.
Question 14. Draw a labeled diagram with necessary switch, regulator, etc. to connect a bulb and a fan with the mains. In what arrangement are they connected to the mains: series or parallel?
Solution:
Parallel connections to the mains are made by these appliances.
Question 15. How should the electric lamps be connected with the mains so that the switching on or off a lamp has no effect on other lamps?
Solution:
In order to prevent the turning on or off of one lamp in a room from having an impact on other lamps in the same building, all the electrical appliances in a building should be linked in parallel at the mains, each with a separate switch and a separate fuse attached in the live wire.
Question 16. In following figure shows three bulbs A, B and C each of rating 100 W, 220 V connected to the mains of 220 V. Answer the following:
(a) How is bulb A connected with the mains? At what voltage does it glow?
(b) How are bulbs B and C connected with the mains? At what the bulb A connected with the mains?
(c) How is the glow of bulbs A and C affected if bulb B gets fused?
(d) How is the glow of bulbs B and C affected if bulb A gets fused?
Solution:
(a) The mains are connected in parallel with Bulb A. When 220 V is put across the bulb, it will begin to glow.
(b) The mains are linked in series with bulbs B and C. The voltage at which they glow will be divided by two from the main’s supply voltage as a result of this series connection to the mains. So, at 110V, bulb B will illuminate.
(c) If bulb B burns out, bulb C that was wired in series with it won’t light up. Due to its parallel connection to the mains, bulb A won’t be affected by this.
(d) The light of bulbs B and C won’t be altered if bulb A fuses.
Question 17. Two sets A and B of four bulbs each are glowing in two separate rooms. When one of the bulbs in set A is fused, the other three bulbs also cease to glow. But in set B, when one bulb fuses the other bulbs continue to glow Explain the difference.
Solution:
The lights are linked in series in set A. As a result, when one bulb’s fuse breaks, the circuit is disrupted and the other lights’ electricity stops flowing. The bulbs are linked in parallel in set B. As a result, each bulb is linked to its designated voltage (in this case, 220 V), and even if the fuse in one bulb blows, the others continue to operate and shine.
EXERCISE-9A
MULTIPLE CHOICE TYPES
Question 1. The main fuse is connected in:
a) Live wire
b) Neutral wire
c) Both the live and earth wires
d) Both earth and the neutral wire.
Solution: (a) Live wire
Question 2. The electrical appliances in a house are connected in:
a) Series
b) Parallel
c) Either in series or parallel
d) Both in series and parallel
Solution: b) Parallel
Question 3. The electric meter in a house records:
a) Charge
b) Current
c) Energy
d) Power
Solution: c) Energy
EXERCISE-9B
Question 1. What is a fuse? Name the material of fuse. State on characteristic of material used for fuse
Solution:
A safety device called an electric fuse is used to control the amount of electricity flowing through an electric circuit. The circuit and the linked appliances are protected from harm by the use of fuses. Due to its low melting point and high resistivity, a lead-tin alloy is utilized as a fuse material.
Question 2. Name the device used to protect the electric circuits from over loading and short circuit. On what effect of current does it work?
Solution:
A safety device called an electric fuse is used to control the amount of electricity flowing through an electric circuit. The circuit and the linked appliances are protected from harm by the use of fuses. Due to its low melting point and high resistivity, a lead-tin alloy is utilized as a fuse material.
Question 3. Complete the following sentence:
(i) A fuse is a short piece of wire of material of high __________ and low __________.
(ii) A fuse wire is made of an alloy of __________ and __________. If the current in a circuit rises too high, the fuse wire__________.
(iii) A fuse is connected in __________ with the __________ wire.
(iv) Higher the current rating, __________is the fuse wire.
(v) Live wire is also called __________ wire.
Solution:
(i) A fuse is a short piece of wire of material of high resistivity and low melting point.
(ii) A fuse wire is made of an alloy of lead and tin. If the current in a circuit rises too high, the fuse wire melts.
(iii) A fuse is connected in series with the live wire
(iv) Higher the current rating, thicker is the fuse wire.
(v) Live wire is also called phase wire.
Question 4. Why is the fuse wire fitted in a porcelain casing?
Solution:
Because porcelain is an electrical insulator, the fuse wire is enclosed in a porcelain case.
Question 5. How is a fuse put in an electric circuit? State the purpose of using a fuse in a circuit.
Solution:
In a porcelain holder, the fuse wire is stretched between the two metallic terminals, T1 and T2 (since porcelain is an insulator of electricity). The porcelain socket that this holder is designed to fit into has two metallic terminals to which the circuit’s live wires are attached. The fuse
Configuration is depicted in the following image.
Each electrical appliance has a fuse attached to it to protect it from an excessive current flow.
Question 6. Describe with the aid of a diagram some form of a fuse which is used in the electric lighting circuit of a house. Give two reasons why a fuse must not be replaced by an ordinary copper wire.
Solution:
In the illustration above, the fuse wire is stretched between the two metallic terminals T1 and T2 in a porcelain holder to represent the most typical fuse layout. The live wire of the circuit is linked to each of the two metallic terminals on the porcelain socket that this holder fits into.
Copper wire cannot be used to replace a fuse because of its extremely low resistance and high melting point.
Question 7. A fuse is always connected to the live wire of the circuit. Explain the reason.
Solution:
The fuse wire is always linked to the circuit’s live wire because if the fuses were placed in the neutral wire, and it burned due to an excessive current flow, the appliance would still be connected to the supply’s high potential point through the live wire. As a result of touching the appliance and coming into contact with the live wire, a person may receive a shock.
Question 8. How does the (i) thickness and (ii) length of a fuse wire depend on its current rating?
Solution:
The current rating of the fuse wire:-
(i) Is directly inversely proportional to the fuse wire’s thickness. The fuse wire’s current rating will be higher the thicker it is.
(ii) The fuse wire’s current rating is independent of its length.
Question 9. Two fuse wire of the same length are rated 5 A and 20 A. Which of the two is thicker and why?
Solution:
To reduce resistance, the 20 A fuse wire will be thicker.
Question 10. Explain the meaning of the statement ‘the current rating of a fuse is 5 A’.
Solution:
It indicates that the line to which this fuse is attached may hold 5 A of electricity.
Question 11. ‘A fuse is rated 8 A’. Can it be used with an electrical appliance of rating 5kW, 200V?
Solution:
Which is more than 8A, It is the maximum safe amount of current that should pass through the electrical equipment. Hence, such a fuse is useless.
Question 12. An electric kettle is rated 3kW, 250V. Give a reason whether this kettle can be used in a circuit which contains a 13A fuse.
Solution:
The safe limit of current for a kettle is, hence this kettle may be used in a circuit with a 13A fuse.
Question 13. What is the purpose of a switch in a circuit? Why is the switch put in the live wire? What precaution do you take while handling a switch?
Solution:
A switch controls how much current flow via a circuit (or in an appliance). In order for the appliance to be linked to the high potential point through the live wire, the switch must always be connected to the live wire. Since the neutral wire serves as the current’s return channel in this place, the circuit is complete. The circuit is broken and no current reaches the appliance in the off position of the switch, when the appliance is not in use.
On the other hand, no electricity flows through the bulb if the switch is linked to the neutral wire and is in the “off” position. However, the live wire links the appliance to the high potential terminal.
As a result, the switch might be misleading to the user and potentially dangerous if it is linked to the neutral line. Switch handling precaution: Avoid touching a switch with moist hands.
Question 14. A switch is not touched with wet hands while putting it on or off. Give a reason for your answer.
Solution:
Wet hands should not be used to operate switches. If water touches the live wire of the switch, it creates a conducting layer between the hand and the live wire, allowing electricity to flow to the hand and potentially deadly shock the person.
Question 15. It is dangerous to connect the switch in the neutral wire. Explain your answer.
Solution:
It is hazardous to connect the switch to the neutral wire when there is an excessive current present. The appliance will continue to be attached to the live wire of a very high potential even if the fuse blows off owing to too much current and the circuit can no longer conduct current. In this scenario, touching the appliance’s body might result in a lethal electric shock. Because of this, connecting the switch to the neutral wire is extremely risky.
Question 16. Draw a circuit diagram using the dual control switches to light a staircase electric light and explain its working.
Solution:
The twin pole type switches known as dual control switches are typically used at the top and bottom of a staircase, or at the opposite ends of a long hallway, etc. Such switches allow the appliance (let’s say a light bulb) to be turned on or off from two distinct locations.
(b) Bulb on through switch S1
(c) Bulb on through switch S2
Figures a, b, and c show a dual control switch’s operation and circuitry. At the top of the stairs, install switch S1. The bulb is shown in the off position in Fig. (a). Now, the switch S1 or the switch S2 may be used individually to turn on the bulb. Switching on S1 changes connection ‘ab’ to ‘bc,’ completing the circuit, and turning on the light [Fig. (b)]. The connection ‘bc’ turns to ‘ba’ when switch S2 is used, once more completing the circuit [Fig. (c)]. In a similar manner, if the bulb is lit as in Fig. (b), it may be turned off by switching the connections “ab” to “bc” using either the switch S1 or the switch S2. When someone uses the switch S1 to turn on the light while climbing a staircase, the connection ‘ab’ switches to ‘bc,’ causing current to flow through the circuit When you reach the top, you turn on the switch S2 to turn off the light, which switches the connection from “cb” to “ba” and stops the flow of electricity.
When someone turns on a light by operating switch S2 to change connection ‘cb’ to ‘ba’ and turns it off by operating switch S1 to convert connection ‘ab’ to ‘bc’, the same system is in operation.
Question 17. What purpose is served by the terminals of a three way pin plug? Draw a diagram and name the pins.
Solution:
Every electrical device comes with a cable with a plug on one end to connect it to the power source. The top pin of this three-way plug is used for earthing (E), followed by the live pin (L) on the left and the neutral pin (N) on the right.
Question 18. The diagram in Fig. 9.27 shows a three pin plug. Label the three pins.
(a) Why if the top pin thicker and longer than the other two?
(b) Why are the pins splitted at the ends?
Solution:
The three pins in the plug are labeled as
Here, the letters
E :- Earth pin
L :- Live wire
N :- Neutral wire.
(a) The earth pin is engineered to be lengthy in order to connect the earth first. Because the fuse will blow out if the device is faulty, this assures the user’s safety. The earth pin is thicker so that it cannot, even accidentally, be put into the socket’s hole for the live or neutral connection.
(b) The pins have a split at the end that acts as a spring to ensure a snug fit in the socket holes.
Question 19. Draw a Labeled Diagram of a Three Pin Socket.
Solution:
E: Earth pin
N: Neutral wire pin
L: Live wire pin
Question 20. The following diagram shows a three pin socket marked as 1, 2 and 3.
(a) Identify and write live (L) neutral (N) and earth (E) against the correct number
(b) To which part of the appliance is the terminal 1 connected?
(c) to which wire joined to 2 or 3, is the fuse connected and why?
Solution:
(a) Here, 1 – Earth, 2 – Neutral, 3 – Live
(b) Terminal 1 is attached to the appliances outside metallic housing.
(c) The fuse is attached to the live wire and linked to pin 3 so that, in the event of an excessive current flow, the fuse melts first and the circuit is broken, protecting the appliances.
Question 21. What do you mean by the term local earthing? Explain how it is done.
Solution:
Close to the kWh metre, local earthing is built. A 2 to 3 metre deep hole is excavated in the earth during this operation. The hole is filled with a copper rod inserted within a hollow insulating pipe. The bottom end of the copper rod is soldered to a thick copper plate that measures 50 cm × 50 cm, and it is then buried in the earth. To create a nice earth, a combination of charcoal and salt is used to round the plate connection.
Water is occasionally put into the pipe to maintain the ground’s moisture. A conducting layer is created between the plate and the ground as a result. At the kWh metre, the copper rod’s higher end is connected to the earth connection.
Question 22. To which wire is the metallic case of an electric appliance connected? Give the reason?
Solution:
If the live wire of a malfunctioning appliance accidentally makes direct touch with the metallic casing, the appliance then develops a high potential live wire. If somebody touches the body of the appliance, they might receive a shock as a result. However, if the appliance is earthed, a strong current travels through the casing to the earth as soon as the live wire makes contact with the metallic housing. The appliance will be removed since the linked fuse will likewise blow.
Question 23. (a) The earthing of an electric appliance is useful only if the fuse is in the love wire. Explain the reason.
(b) Name the part of the appliance which is earthed.
Solution:
(a) Only the live wire must be connected to the fuse. If the fuse is in the neutral wire, the appliance will still be operating at supply voltage even if the fuse will burn owing to the high current flow. As a result, when the device is touched, current will flow from the appliance to the person contacting it.
(b) The appliance’s metallic casing has to be grounded.
Question 24. For earthing an electrical appliance, one has to remove the paint from the metal body of the appliance where the electrical contact is made. Explain the reason.
Solution:
The paint acts as an insulating coating on the appliance’s metal body. Therefore, the paint must be removed from the body area where connection is to be established in order to make an earth connection.
Question 25. What is the colour code for the insulation on the (a) live (b) neutral and (c) earth wire?
Solution:
According to new international convention:-
(a) The colour of the live wire is brown.
(b) Earth wire is yellow or green in colour.
(c) Earth wire is yellow or green in colour.
Question 26. Name the colour code of the wire which is connected to (i) metallic body of an appliance, (ii) switch for the appliance.
Solution:
Colour code of the wire which is connected to
(i) The earthing wire, which is green in colour, is attached to an appliance’s metallic body.
(ii) The red, live wire serves as the appliance’s switch.
Question 27. How does the colour code of wires in a cable help in house wiring?
Solution:
In house wiring, the color-coding of the wires makes it easier to connect the switch, fuse, sockets, etc. using the correct wire.
Question 28. A power circuit uses a cable having three different wires.
(a) Name the three wires of the cable.
(b) To which of the two wires should the heating element of an electric geyser be connected?
(c) To which wire should the metal case of the geyser be connected?
(d) To which wire should the switch and fuse be connected?
Solution:
(a) The Live wire, Earth wire, and Neutral wire are the three wires.
(b) The geyser’s heating element has to be wired into both the live and neutral conductors.
(c) The metal casing has to be wired to the ground.
(d) Live wire should be connected to the switch and fuse.
Question 29. State two circumstances when one may get an electric shock from an electrical gadget. What preventive measure must be provided with the gadget to avoid it?
Solution:
In the following two scenarios, an electrical device might shock a person:
(i) If the fuse is installed in the neutral wire rather than the live wire and, due to a fault, an excessive amount of current flows through the circuit, the fuse burns, current ceases to flow through the circuit, but the appliance is still connected to the supply’s high potential point via the live wire. In this case, touching the defective device may result in an electric shock since the individual would be in contact with the live wire.
(ii) When a defective appliance’s live wire comes into touch with its metallic casing directly because the insulation has broken after prolonged usage (or for other reasons), the device gains the high potential of the live wire. Because current travels from his body to the soil, anyone who touches it will receive a shock.
Preventative measure: The electric appliance has to be properly “earthed.”
Question 30. Why is it necessary to have an earth wire installed in a power circuit, but not in a lighting circuit?
Solution:
High-power and expensive devices are carried by power circuits. The gadget may be harmed if there is an unwanted power signal (noise) in the connection. Earth is required in order to lessen this impact.
Low-power circuits are used for lighting (current). We thus disregard the earth terminal.
Question 31. Give two characteristics of a high tension wire.
Solution:
A high tension wire has a big surface area and less resistance.
Question 32. Which of the cables, one rated 5A and the other 15 A will be of thicker wire? Give a reason for your answer.
Solution:
The wire’s resistance should be low in order to carry more current, which calls for a wide cross sectional area. Thus, wire with a 15A current rating will be thicker.
Question 33. The following diagram shows three lamps and three switches 1, 2 and 3
(a) Name the switch/switches to be closed so as to light all three lamps.
(b) How are the lamps connected: in series or in parallel?
Solution:
(a) Switches 2 and 3.
(b) The lamps are connected in series.
Question 34. In the following Figure shows two bulbs with switches and fuse connected to mains through a socket.
(i) Label each component
(ii) Name and state the color of insulation of each wire 1, 2, and 3.
(iii) How are the two bulbs joined: in series or in parallel?
Solution:
(i)
(ii)
(iii) The bulbs are connected in series.
EXERCISE-9B
MULTIPLE CHOICE TYPES
Question 1. The rating of a fuse connected in the lighting circuit is :
a) 15A
b) 5A
c) 10 A
d) Zero
Solution: b) 5A
Question 2. A switch must be connected in:
a) Live wire
b) Neutral wire
c) Earth wire
d) Either earth or neutral wire
Solution: a) A switch must be connected in live wire.
