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This is one of our many quizzes on Electromagnet. Click on this to access more such competitive quizzes on Current Electricity and EMI.

Electromagnet Quiz 2

physics

Which of the following is true for a soft iron core? 

Soft iron is used for making electromagnets. It is because it does not retain its magnetism when the current is switched off, which means that it does not become permanently magnetized and it gets magnetized more easily when we apply the external field. 

  The tendency to maintain magnetic fields even when external fields are removed is referred to as retentivity. Susceptibility defines how often a substance can become magnetized if an external field is applied. Soft iron, on the other hand, is widely used in the manufacturing of electromagnets since it does not maintain magnetism until the current supply is cut off. When we add the exterior field, it also magnetizes more quickly. That means, It has a low retentivity and a high susceptibility. Therefore both option (a) and (b) are correct.

When a current carrying conductor is placed in a magnetic field, it experiences a force. What adjustment should be made such that the force experienced by the conductor is greatest?

A current carrying conductor placed in a magnetic field will experience magnetic Lorentz force. This force is given by the product of current carried by the conductor and the cross product between length of the conductor and magnetic field. Cross product is given by the sine of angle between the vectors. This angle will determine the strength of the experienced force.As $F=BIl\sin \theta$ this indicates that $F\propto \sin \theta$.

  If a current carrying conductor of length l  is placed in a magnetic field of $\overrightarrow{B}$ at an angle $\theta$ then it will experience a torque. This torque arises due to the couple of magnetic Lorentz forces acting at each end of the current carrying conductor. $ \\ $ This force is given by the equation,$ \\F=I\left( \overrightarrow{l}\times \overrightarrow{B} \right) \\\Rightarrow F=BIl\sin \theta  \\\Rightarrow F\propto \sin \theta  \\ $ Then, to make the force experienced by the conductor to be maximum, we will have to keep it at $90{}^\circ$. That means it must be placed perpendicular to the magnetic field. Now, if we keep it at $0{}^\circ$ that means parallel to the field, the force experienced will be zero. $ \\ $  <img  src="https://cmds-vedantu.s3.ap-southeast-1.amazonaws.com/prod/question-sets/82379835-b0a1-43ec-810c-3f5e7cb800cd4389152679844075469.png"/>

An electromagnet with a magnetic field strength of $250\text{ Ampere }{{\text{m}}^{-1}}$ having a length of $20cm$ and a current of $1A$ is flowing through it. Find the number of turns? 

Magnetic field intensity of an electromagnetic coil increases with the increase in number of turns.It is directly proportional to the number of turns per unit length and current passing through the coil i.e, $B={{\mu }_{0}}nI$ 

 Magnetic field produced by an electromagnet of length l and number of turns N having a current I is given by the equation, $ B={{\mu }_{0}}nI$. But here, $n$ is the number of turns per unit length. It is given by $n=\dfrac{N}{l}$. $ \\ $ Then, magnetic field will be, $ \\B={{\mu }_{0}}\times \dfrac{N}{l}\times I\\ $ Now, by rearranging this equation, we can find the expression for the number of turns. $ \\N=\dfrac{Bl}{{{\mu }_{0}}I} \\\Rightarrow N=\dfrac{250\times 20\times {{10}^{-2}}}{1.25663706\text{ }\times \text{ }{{10}^{-6}}\times 1} \\\Rightarrow N=\dfrac{50}{1.25663706\text{ }\times \text{ }{{10}^{-6}}} \\\therefore N=39.79\times {{10}^{6}}\approx 40\times {{10}^{6}}\text{ turns}$ 

 A Gold thin rod of length $13\,m$, carrying current of $3A$ is placed in a parallel orientation to a magnetic Field of $9\,Tesla$. Find the amount of force experienced by it.

If a current carrying conductor of length $l$  is placed in a magnetic field of $\overrightarrow{B}$ at an angle $\theta $ , then it will experience a torque due to a couple of magnetic Lorentz forces. 

 <img  src="https://cmds-vedantu.s3.ap-southeast-1.amazonaws.com/prod/question-sets/fc85b445-94fc-419f-bbe0-b06944379a124729317407364316190.png"/> $ \\ $ A current carrying conductor placed in a magnetic field will experience magnetic Lorentz force. This force is given by the product of current carried by the conductor and the cross product between the length of the conductor and magnetic field. $ \\F=I\left( \overrightarrow{l}\times \overrightarrow{B} \right) \\\Rightarrow F=BIl\sin \theta  \\ $ Here, the rod is placed parallel to the magnetic field. Then, the angle between $ \overrightarrow{l}\,\text{and}\,\overrightarrow{B}\,\text{will be}\,0{}^\circ.\\F=I\left( \overrightarrow{l}\times \overrightarrow{B} \right) \\\Rightarrow F=BIl\sin \theta  \\\Rightarrow F=9\times 3\times 13\times \sin \left( 0 \right) \\\therefore F=0\,N$ 

 Which of the following is the major drawback of electromagnets? 

Magnetic field produced by passing electricity through a conductor is known as an electromagnet.An electromagnet can be turned OFF at will and it is the major reason why we use electromagnets in so many of its applications. Also, the strength of an electromagnet can be controlled. 

 Electromagnets are magnets that are formed with an electric current. It can be activated or deactivated by adjusting the electric current. When an electric current is passed through a coil or a cable, it generates a magnetic field around it. If we want to increase the field's intensity, we simply increase the number of windings. $ \\ $ The biggest downside of an electromagnet is that as we transfer energy through the coil, it heats up due to the coil's resistance. Furthermore, an electromagnet is not like an ordinary magnet except that it has magnetic properties all of the time. It turns into a magnet only when we pass electricity through it. $ \\ $ As a consequence, it needs a continuous supply of electricity. One of the major reasons we use electromagnets is that they can be switched on and off at will. As a result, it is the most significant benefit of having an electromagnet. So, from the options, the only statement in option $(b)$ is the drawback of an electromagnet.