Mix Examples - Magnetic Effects of Electric Current Questions in English

(D) The magnetic force $F$ acting on a current-carrying conductor placed in a magnetic field is given by the formula $F = I L B \sin(\theta)$.
Here,$I$ is the electric current,$L$ is the length of the conductor within the magnetic field,$B$ is the magnetic field strength,and $\theta$ is the angle between the current direction and the magnetic field.
Since the wire is placed perpendicular to the magnetic field,$\theta = 90^\circ$,and $\sin(90^\circ) = 1$.
Therefore,the force $F = I L B$.
This shows that the magnetic force is directly proportional to the electric current $(I)$,the length of the wire $(L)$,and the magnetic field strength $(B)$.
Thus,all the given options are correct.

(A) When a current-carrying conductor is placed in a magnetic field,it experiences a magnetic force.
According to Fleming's Left-Hand Rule,if we stretch the thumb,forefinger,and middle finger of our left hand such that they are mutually perpendicular to each other,then the forefinger points in the direction of the magnetic field,the middle finger points in the direction of the current,and the thumb gives the direction of the force acting on the conductor.
Therefore,Fleming's Left-Hand Rule is used to determine the direction of the magnetic force.

(A) An electromagnet is used in cranes to lift heavy loads like cars in junkyards.
This is because an electromagnet can be turned on and off by controlling the electric current.
When the current is switched on,the crane becomes magnetic and picks up the metal object.
When the current is switched off,the magnetic field disappears,allowing the load to be released easily.

(D) The phenomenon that a current-carrying conductor experiences a force when placed in a magnetic field was first observed by $Andre-Marie$ $Ampere$.
He demonstrated that magnetic fields exert forces on moving charges,which results in a mechanical force on the conductor carrying the current.

(A) The force $F$ acting on a current-carrying conductor placed in a magnetic field is given by the formula $F = BIl \sin(\theta)$,where $B$ is the magnetic field strength,$I$ is the current,$l$ is the length of the conductor,and $\theta$ is the angle between the direction of the current and the magnetic field.
When the direction of the current is perpendicular to the magnetic field,the angle $\theta = 90^\circ$.
Since $\sin(90^\circ) = 1$,the force becomes $F = BIl(1) = BIl$.
This value represents the maximum force that can act on the conductor.

(D) The magnetic field $B$ at the center of a circular current-carrying loop is given by the formula $B = \frac{\mu_0 I}{2R}$,where $\mu_0$ is the permeability of free space,$I$ is the current,and $R$ is the radius of the loop.
From this formula,it is clear that the magnetic field $B$ is inversely proportional to the radius $R$ $(B \propto \frac{1}{R})$.
Since the current $I$ is the same for all loops,the loop with the smallest radius will have the strongest magnetic field at its center.
Comparing the given radii ($1 \; CM$,$2 \; CM$,$3 \; CM$,and $4 \; CM$),the smallest radius is $1 \; CM$.
Therefore,the loop with a radius of $1 \; CM$ will have the strongest magnetic field at its center.

(A) An electric motor is a device that converts electrical energy into mechanical energy.
It works on the principle that when a rectangular coil carrying current is placed in a magnetic field,it experiences a magnetic force,which causes the coil to rotate.

(B) In an electric motor,a large number of turns of insulated copper wire wound on a soft iron core is called an $Armature$.
This $Armature$ is placed on an axis and rotates within a magnetic field when current flows through it.

(D) An electric motor is a device that converts electrical energy into mechanical energy.
Mixers,electric fans,and washing machines all utilize electric motors to produce rotational motion for their operation.
An electric bell,however,works on the principle of electromagnetism using an electromagnet to attract a clapper,which strikes the gong. It does not use a rotating electric motor.

(A) An electric generator is a device that converts mechanical energy into electrical energy.
It operates on the principle of electromagnetic induction,where a conductor moving in a magnetic field induces an electric current.
In contrast,an electric motor converts electrical energy into mechanical energy.
Electric irons and ovens convert electrical energy into heat energy.

(C) Electromagnetic induction is the phenomenon where a changing magnetic field induces an electromotive force $(EMF)$ or current in a conductor.
An electric generator works on the principle of electromagnetic induction,where mechanical energy is converted into electrical energy by rotating a coil within a magnetic field.
In contrast,an electric motor works on the principle of the magnetic effect of current (force on a current-carrying conductor in a magnetic field).
Therefore,the correct option is $C$.

(A) According to Faraday's law of electromagnetic induction,the induced electromotive force $(e)$ in a loop is given by $e = -\frac{d\phi}{dt}$,where $\phi$ is the magnetic flux linked with the loop.
Since the induced current $I = \frac{e}{R}$ (where $R$ is the resistance of the loop),the induced current is directly proportional to the rate of change of magnetic flux,i.e.,$I \propto \frac{d\phi}{dt}$.
Therefore,the induced current is maximum when the rate of change of magnetic flux $(\frac{d\phi}{dt})$ is maximum.
This occurs when the magnetic field linked with the loop changes rapidly.

(A) According to Faraday's Law of Electromagnetic Induction,the induced $EMF$ $(\varepsilon)$ in a coil is given by the formula: $\varepsilon = -N \frac{d\Phi_B}{dt}$.
Here,$N$ is the number of turns in the coil and $\frac{d\Phi_B}{dt}$ is the rate of change of magnetic flux.
The magnetic flux $\Phi_B$ depends on the magnetic field strength and the area of the coil,which is influenced by the speed of the magnet and the number of turns.
The shape of the coil does not directly determine the magnitude of the induced $EMF$ in this context,as the $EMF$ depends on the total flux linkage and the rate of change,not the geometric configuration of the wire itself.

(B) In an electric generator,a split ring (commutator) is used to reverse the direction of the current in the coil after every half rotation,which ensures that the output current flows in a single direction $(DC)$.
If a full circular ring (slip ring) is used instead of a split ring,the direction of the induced current in the coil reverses after every half rotation without being rectified.
Consequently,the current flowing through the external circuit changes its direction periodically,resulting in the production of alternating current $(AC)$.

(D) In most power plants (such as thermal,hydroelectric,or nuclear power plants),electricity is generated by rotating a turbine connected to a generator. The generator works on the principle of electromagnetic induction,where a changing magnetic field induces an electromotive force $(EMF)$ in a coil,thereby producing electricity.

(A) Fleming's Left-Hand Rule is used to determine the direction of the force acting on a current-carrying conductor placed in a magnetic field.
According to this rule,if we stretch the thumb,forefinger,and middle finger of the left hand such that they are mutually perpendicular to each other:
$1$. The forefinger points in the direction of the magnetic field.
$2$. The middle finger points in the direction of the current.
$3$. The thumb points in the direction of the force (or motion) acting on the conductor.
Therefore,the thumb indicates the direction of the magnetic force.

(A) In a $DC$ electric motor,a split-ring commutator is used to reverse the direction of the current flowing through the coil after every half rotation.
This reversal of current ensures that the force acting on the coil continues to push it in the same direction,allowing the motor to rotate continuously.
Therefore,the correct answer is half rotation.

(C) Fleming's right-hand rule is used to determine the direction of the induced current in a conductor moving in a magnetic field.
According to this rule,if we stretch the thumb,forefinger,and middle finger of the right hand such that they are mutually perpendicular to each other:
$1$. The thumb points in the direction of the motion of the conductor.
$2$. The forefinger points in the direction of the magnetic field.
$3$. The center (middle) finger points in the direction of the induced electric current.

(A) An electric bell works on the principle of the magnetic effect of electric current,specifically using an electromagnet.
When the switch is pressed,the electric current flows through the coil,which acts as an electromagnet.
This electromagnet attracts the iron armature,causing the hammer to strike the gong.
As the armature moves,the circuit is broken,the electromagnet loses its magnetism,and the spring pulls the armature back,completing the circuit again to repeat the process.

(C) fire alarm system typically utilizes an electric bell as an output device to produce a loud sound when a fire is detected. The electric bell operates on the principle of the magnetic effect of electric current. When the circuit is closed by a sensor (like a heat or smoke detector),current flows through the electromagnet,which attracts the hammer to strike the gong,creating a continuous alarm sound.

(B) According to Fleming's Right-Hand Rule:
$1$. The forefinger points in the direction of the magnetic field $(X)$.
$2$. The thumb points in the direction of the motion of the conductor $(Y)$.
$3$. The middle finger points in the direction of the induced current $(Z)$.
Therefore,$X$ is the forefinger,$Y$ is the thumb,and $Z$ is the middle finger.

(D) Direct Current $(DC)$ is a type of electric current that flows in only one direction.
Unlike Alternating Current $(AC)$,which periodically reverses its direction and magnitude,$DC$ maintains a constant polarity and magnitude over time.
Frequency is defined as the number of cycles per second of an alternating waveform.
Since $DC$ voltage does not oscillate or change its direction,it does not complete any cycles.
Therefore,the frequency of $DC$ voltage is $0 \ Hz$.

(B) In the United States of America $(USA)$,the standard domestic electrical power supply is provided at a voltage magnitude of $110\;V$ and a frequency of $60\;Hz$.
In contrast,many other countries,including India,use a standard voltage of $220\;V$ to $240\;V$ with a frequency of $50\;Hz$.
Therefore,the correct option is $B$.

(A) In domestic electrical circuits,standard color coding is used for safety and identification.
$1$. The $Red$ wire is used for the $Live$ (or $Phase$) connection,which carries the current from the power supply.
$2$. The $Black$ wire is used for the $Neutral$ connection.
$3$. The $Green$ or $Yellow$ wire is used for $Earthing$ (grounding) to prevent electric shocks.
Therefore,the red-colored insulated wire is used for the $Live$ connection.

(B) According to the standard color coding for domestic electrical wiring in India:
$1$. The $Live$ wire is typically red.
$2$. The $Neutral$ wire is typically black.
$3$. The $Earth$ wire is typically green.
Therefore,the correct color for the neutral wire is black.

(C) Direct current $(DC)$ is a unidirectional flow of electric charge.
Most electronic devices that contain batteries or sensitive electronic circuits,such as a cellphone,operate on $DC$.
Appliances like refrigerators,tubelights,and electric fans typically run on alternating current $(AC)$ supplied by the power grid.

(D) In domestic electrical circuits,two types of circuits are used: one with a $5A$ current rating for appliances with lower power consumption (like bulbs,fans,and televisions) and another with a $15A$ current rating for appliances with higher power consumption (like air conditioners,refrigerators,and electric irons).
Therefore,appliances with higher power ratings are connected to the $15A$ line.

(B, C, D) In domestic electrical circuits,two types of circuits are used: a $5\, A$ circuit for low-power appliances and a $15\, A$ circuit for high-power appliances.
Appliances like $TV$,tubelights,and electric fans consume very little power and are designed to operate on a $5\, A$ circuit.
Connecting these low-power devices to a $15\, A$ line is unnecessary and potentially unsafe if the circuit protection is not properly matched.
An air conditioner is a high-power appliance that requires a $15\, A$ circuit.
Therefore,$TV$,tubelight,and electric fan are not typically connected to a $15\, A$ line,but among the given options,the question implies identifying appliances that do not require such high current capacity. Since $TV$,tubelight,and electric fan all fall into this category,the question is slightly ambiguous; however,in standard practice,$TV$,tubelight,and fan are all $5\, A$ appliances.

(A, C, D) Power rating refers to the amount of electrical energy an appliance consumes per unit of time $(P = V \times I)$.
Appliances like $TV$s generally have a lower power rating (typically $50 \ W$ to $200 \ W$).
Appliances like Geysers,Heaters,and Air conditioners are high-power appliances that require significant electrical energy to generate heat or cooling,often ranging from $1000 \ W$ to $3000 \ W$ or more.
Among the given options,$TV$ is the only appliance with a low power rating,while Geysers,Heaters,and Air conditioners are high-power appliances. However,the question asks which one is $NOT$ of lower power rating. Since Geysers,Heaters,and Air conditioners are all high-power,this question implies identifying the high-power category. Given the standard classification,Geysers,Heaters,and Air conditioners are all high-power. If we must choose one that is typically the highest or most representative of high-power,Air conditioners often have the highest rating,but all three ($A$,$C$,$D$) are high-power compared to a $TV$.

(B) When too many electrical appliances are connected to a single circuit,the total current drawn from the source exceeds the capacity of the wires. This excessive flow of current causes the wires to heat up significantly,which can lead to damage or fire. This phenomenon is known as $Overloading$.

(D) An electric fuse is a safety device used in electrical circuits.
It consists of a wire made of a material with a low melting point.
When an excessive amount of current flows through the circuit due to short-circuiting or overloading,the fuse wire heats up and melts.
This breaks the circuit,thereby preventing the flow of current to the appliances.
Thus,it protects the electrical appliances from damage caused by high current surges.

(C) fuse wire is a safety device used in electrical circuits to protect appliances from high current.
It must have a low melting point so that it melts and breaks the circuit when the current exceeds a safe limit.
Nichrome is an alloy with a very high melting point and high resistance,which is why it is used as a heating element in appliances like heaters and toasters,not as a fuse wire.
Pure tin,lead,and alloys of tin and lead have low melting points,making them suitable for fuse wires.