Exercise Question 1.
Tell the odd one out. Give a proper explanation.
a. Fuse wire, bud conductor, rubber gloves, generator.
Answer. The generator changes mechanical energy into electrical energy, while the other three do not.
b. Voltmeter, Ammeter, galvanometer, thermometer.
Answer: The thermometer measures the temperature and the remaining three measure electric quantities.
c. Loud speaker, microphone, electric motor, magnet.
Answer:
Magnet. It exerts a force on a magnetic material, the remaining three convert one form of energy into another.
Effects Of Electric Current Exercise Question 2.
Explain the construction and working of the following. Draw a neat diagram and label it.
a. Electric motor
b. Electric Generator (AC)
Answer. An electric motor is a device that converts electrical energy into mechanical energy by utilizing the principle that a current-carrying coil placed in a magnetic field experiences a force and begins to rotate.
The construction of an electric motor involves a rectangular loop made of copper wire with a layer of resistance on its surface, forming the ABCD loop.
When the circuit is activated, an electric current move through the conductor, starting from point E and passing through the copper loop in the sequence E → A → B → C → D → F. The magnetic field influences the loop, directing power from the north pole to the south pole.
Following Fleming’s left-hand rule, the interaction between the magnetic field and the current-carrying conductors creates distinct forces on the AB and CD branches of the loop. The force on AB directs it downwards, while the force on CD pushes it upwards, both with equal magnitude but in opposite directions. As the loop ABCD and the axle rotate, an anticlockwise motion is evident from the side AD, demonstrating the harmonious interplay between electrical energy, magnetic fields, and the principles of electromagnetism. Upon completing half a rotation, a remarkable transformation occurs as points X and Y, previously separated by split rings, make contact with brushes F and E, respectively. This alters the current flow, redirecting it through the loop in the sequence EDCBAF.
Once again, the magnetic field influences the loop, this time directing power from the south pole towards the north pole. As a result, the forces acting on AB and CD reverse direction, with the force on CD directing it downwards and the force on AB pushing it upwards. Despite the reversal in force direction, the loop and axle continue their anticlockwise rotation, undeterred by the change.
This unwavering motion showcases the inherent momentum imparted by the initial rotation. With each subsequent half rotation, the current in the loop dutifully reverses direction, ensuring that the loop and axle maintain their unwavering anticlockwise spin. This perpetual interplay of electrical currents, magnetic fields, and rotating conductors continues until the external power source is switched off. When the current is abruptly stopped, the loop and axle gradually lose their momentum. The anticlockwise rotation slows and eventually comes to a complete stop, leaving the loop suspended in stillness.
(b) Electric Generator (AC)
Answer. In the diagram, picture a coil of copper wire labelled ABCD placed strategically between the strong magnetic poles N and S of a powerful magnet. The ends of the coil are connected to two conducting rings, R1 and R2, through carbon brushes B1 and B2. These rings, firmly fixed to the axle, have a thin layer of resistance on their inner surfaces. Fixed brushes, linked to a galvanometer, are prepared to determine the direction of current flow in the circuit.
When an external force sets the axle in motion, the coil ABCD begins a rhythmic rotation. Assuming the coil rotates clockwise as seen from side AD, branch AB ascends while branch CD descends simultaneously. This synchronized movement triggers a series of events governed by electromagnetism principles.
Fleming’s right-hand rule, a key principle in electromagnetism, determines the direction of the induced current. In this case, the induced current flows in the sequence A → B → C → D. As the current travels through the external circuit, it goes from B2 to B, passing through the vigilant galvanometer. The strength of this induced current is directly proportional to the number of turns of copper wire carefully wound around the coil.
After completing half a rotation, AB and CD swap positions, creating a captivating dance of conductors within a magnetic field. This exchange results in a reversal of the induced current’s direction, guiding it along the path D → C → B → A. With AB remaining in constant contact with B1 and CD connected to B2, the current in the external circuit smoothly flows from B1 to B2, once again passing through the galvanometer. This remarkable phenomenon of alternating current generation stems from the continuous repetition of this half-rotation cycle. The magnetic field, acting as an invisible conductor’s baton, orchestrates the rhythmic flow of electrons, leading to the generation of alternating current (AC)
Question 3
Electromagnetic induction means
a. Charging of an electric conductor.
b. Production of magnetic field due to a current flowing through a coil.
c. Generation of a current in a coil due to relative motion between the coil and the magnet.
d. Motion of the coil around the axle in an electric motor.
Answer:
c. Generation of a current in a coil due to relative motion between the coil and the magnet.
Electric Current Question 4.
4. Explain the difference between AC generator and DC generator.
Answer. AC generators do not use split rings and the current direction changes periodically.
On the other hand, DC generators use split rings, and the current flows consistently in one direction.
Question 5.
Which device is used to produce electricity? Describe with a neat diagram.
(1) Electric motor
(2) Galvanometer
(3) Electric generator (DC)
(4) Voltmeter
Dc generator
Operation: A machine rotates the axle externally. As the generator’s armature coil spins within the magnetic field, electromagnetic induction generates an electric potential difference in the coil. This results in a current, indicated by a glowing bulb or galvanometer. The current’s direction is determined by the coil’s rotation. In a DC generator, one brush always touches the upward-moving arm of the coil, while the other brush touches the downward-moving arm in the magnetic field. Consequently, the current in the circuit always flows in the same direction as long as the coil
rotates within the magnetic field. In a DC generator, the current flows consistently in one direction throughout the coil’s rotation. However, the current’s magnitude fluctuates periodically over time, distinguishing it from the current produced by an electric cell.
Question 6. How does the short circuit form? What is its effect?
Answer. When a bare live wire and a bare neutral wire touch or come close, the circuit’s resistance decreases, allowing a large amount of electric current to flow, causing a short circuit. This can lead to a significant increase in temperature within the components, potentially resulting in a fire.
Question 7. Give scientific reasons:
a. Tungsten is used to make a solenoid-type coil in an electric bulb.
Answer: 1. The brightness of the light produced by a bulb’s filament is directly linked to the filament’s temperature, which rises as the temperature increases.
2. A bulb’s filament material must have a high melting point to sustain the heat generated by an electric current without melting, allowing for increased light output. Tungsten, known for its high melting point, is commonly utilized for this purpose in electric bulbs.
b. In the electric equipment producing heat e.g. iron, electric heater, boiler, toaster, etc. an alloy such as Nichrome is used, not pure metals.
Answer. 1. Heating devices like toasters and electric irons operate by converting electric energy into heat through the passage of electric current in a metallic conductor.
2. Alloys like Nichrome have high resistivity and can reach high temperatures without oxidizing, unlike pure metals. As a result, the coils in heating appliances such as toasters and electric irons are typically made from an alloy like Nichrome instead of pure metals.
c. For electric power transmission, copper or aluminium wire is used.
Answer. 1. Copper and aluminium are excellent electricity conductors.
2. Copper and aluminium exhibit minimal resistance, resulting in low heat generation when an electric current passes through them. This makes copper or aluminium wires ideal for transmitting electric power.
d. In practice the unit kWh is used for the measurement of electric energy, rather than the joule.
Answer. Various electrical appliances consume a significant amount of electricity, requiring a precise measuring system. Julie is lower in value compared to kilowatt-hours (1 kWh = 3.6 × 10^6 J), hence why we utilize kWh for electricity measurement.
Question 8.
Which of the statements given below correctly describes the magnetic field near a long, straight current-carrying conductor?
(1) The magnetic lines of force are in a plane, perpendicular to the conductor in the form of straight lines.
(2) The magnetic lines of force are parallel to the conductor on all sides of the conductor.
(3) The magnetic lines of force are perpendicular to the conductor going radially outward.
(4) The magnetic lines of force are in concentric circles with the wire as the centre, in a plane perpendicular to the conductor.
Question 9. What is a solenoid? Compare the magnetic field produced by a solenoid with the magnetic field of a bar magnet. Draw neat figures and name various components.
Answer: A copper wire with a resistive coating wound in a chain of loops, like a spring, is referred to as a solenoid.
The magnetic field lines generated by a current-carrying solenoid are comparable to those of a bar magnet. In this setup, one face of the coil functions as the south pole while the opposite face serves as the north pole.
Magnetic lines of force around a bar magnet
By utilizing a current-carrying coil, similar to a magnet, one can magnetize materials such as carbon steel or chromium steel rods. With a sufficiently strong magnetic field, permanent magnetism can be induced in these materials.
Question 10. Name the following diagrams and explain the concept behind them.
Answer:
(a) Fleming’s right-hand rule:
Extend the right hand’s thumb, index finger, and middle finger so they form a right angle. The thumb points in the conductor’s motion direction, the index finger shows the magnetic field direction, and the middle finger indicates the induced current’s direction.
(b) Fleming’s Left-Hand Rule
Answer. The thumb, index finger, and middle finger of the left hand are extended to form a perpendicular arrangement. When the index finger aligns with the magnetic field and the middle finger points in the direction of the current, the thumb indicates the force on the conductor.
A magnetic field applies force to a current-carrying conductor, as electric current represents the flow rate of electric charge. This force is utilized to propel charged particles like protons, deuterons, alpha particles, and electrons to high energies. Devices known as charged particle accelerators, which can be linear or circular and substantial in size, are employed for this purpose. These high-energy particles are instrumental in exploring matter’s structure.
Question 11. Identify the figures and explain their use.
Answer.
(a) Fuses
A fuse safeguards electrical circuits and devices by interrupting the electric current flow when it surpasses a set limit. It is installed in series with the device or circuit to provide protection. Typically, a fuse consists of a wire made from a low melting point alloy, like lead and tin. If the current exceeds the predetermined value, the fuse wire heats up and melts, breaking the circuit and preventing damage to the device. The fuse wire is commonly enclosed in an insulating cartridge, such as glass or porcelain, with metal caps. The current rating (e.g., 1A, 2A) may be indicated on the cartridge.
(b)Miniature Circuit Breakers (MCBs)
Answer. Miniature circuit breaker (MCB) switches are commonly utilized in modern households to interrupt the flow of current in case of a sudden increase. Various types of MCBs are available, although traditional fuse wires are still commonly used to safeguard the entire house.
(c) Generation of a current in a coil due to relative motion between the coil and the magneta
Here, instead of a bulb, an ammeter is displayed. Operation: The axle is turned by an external machine. As the armature coil of the generator spins within the magnetic field, an electric potential difference is generated in the coil through electromagnetic induction. This results in a current, indicated by the illumination of the bulb or by a galvanometer.
The current’s direction is contingent upon the coil’s rotation direction. In a DC generator, one brush is in constant contact with the upward-moving arm of the coil, while the other brush touches the downward-moving arm of the coil within the magnetic field. Consequently, the current in the circuit always flows in the same direction, as long as the coil continues its rotation in the magnetic field.
12 .Solve the following example.
a. Heat energy is being produced in a resistance in a circuit at the rate of 100 W. The current of 3 A is flowing in the circuit. What must be the value of the resistance?
Heat (Power) = Current^2 xResistance
We can rearrange this formula to find the resistance:
Resistance = Heat / Current^2
Plugging in the numbers we know:
Resistance = 100 W / (3 A)^2
Resistance = 100 W / 9 A^2
Resistance ≈ 11.11 Ω (Ω is the symbol for ohms, the unit of resistance)
(b).Two tungsten bulbs of wattage 100 W and 60 W power work on 220 V potential difference. If they are connected in parallel, how much current will flow in the main conductor?
Answer. Let’s imagine electricity flowing through a wire like water flowing through a pipe. In this case, the “pipe” is the circuit, and the “water” is the electric current.
The formula that relates power (wattage), voltage, and current is:
Power=Voltage×Current
We can rearrange this formula to solve for current:
Current = Power/ Voltage
For 100-watt bulb
Current 1=100/220
For 60-watt bulb
Current 2=60/220
When bulbs are connected in parallel, the total current is the sum of the currents through each bulb:
Total Current=Current1+Current2
Total Current = 100/220 +60/220
Total Current=160/220
Total current =8/11
= 0.72 Answer.
c. Who will spend more electrical energy? 500 W TV set in 30 mins, or 600 W heater in 20 mins?
Solution 500 W TV set used for 30 minutes
30 minutes means half an hour can be written as ½
600 W heater for 20 mins so 20 minutes = 20/60
Which is 1/3 by reducing 20/60
So 500 x ½ = 250 W.h
600 W heater 600 x 1/3 = 200 w.h
So TVset will consume more electricity.
d. An electric iron of 1100 W is operated for 2 hours daily. What will be the electrical consumption expenses for that in the month of April? (The electric company charges ₹ 5 per unit of energy.)
Solution. Electric iron 1100W operated for 2 hours
In April there are 30 days so 2 x 30 = 60 h
Energy expenses RS 5 per unit =?
N= Pt/ 100W.h/unit =1100 Wx 60 h/ 1000w.h /unit
Consumption 66 unit x 5 per unit =330 R.S