Explain how crossed E → and B → fields serve as a velocity selector.

A velocity selector is an arrangement of electric and magnetic field so that the charge of a particular velocity moves undeflected in electric and magnetic field. We know that, a stationary charged particle experiences a force F in an electric field only but a moving charged particle experiences a force both in electric E and magnetic field B . This is called the Lorentz force, given by: F → = q E → + v → × B → ....(i) Let the electric field vector, magnetic field vector and velocity vector be mutually perpendicular as shown in the figure drawn above. Hence, these can be written as: E → = E j ^ ; B → = B k ^ ; v → = v i ^ Hence, the force due to the electric field can be written as: F → E = q E → = q E j ^ ......(ii) Force due to the magnetic field can be written as: F → B = q v → × B → = q v i ^ × B k ^ = - q v B j ^ ....(iii) From (ii) and (iii), it is clear that the electric and magnetic fields are opposite in direction. If the magnitude of electric and magnetic fields are so adjusted that they become equal then the total force on the charge is zero and the charge with the velocity v will move deflected. Hence, the condition for the charge to move undeflected is: q E = q v B ⇒ v = E B .......(iv)

How do you convert a moving coil galvanometer into an ammeter?

For using a galvanometer to measure currents, a small resistance called shunt resistance r s is added in parallel to the galvanometer coil. In this way, most of the current pass through shunt. Thus, the problem due to the high resistance of the galvanometer R G is eliminated. Secondly, being a sensitive device the galvanometer shows full-scale deflection for a current of the order of μA . For this, the scale is calibrated and then graduated to read off the current value with ease.

Distinguish between ammeter and voltmeter.

S.N. Ammeter Voltmeter 1. It is used to measure current in a circuit. An ideal ammeter has zero resistance. It is used to measure the potential difference across a given section of the circuit. An ideal voltmeter has infinite resistance. 2. It is always connected in series in a circuit. It is connected in parallel in the section of the circuit. 3. To convert a galvanometer into an ammeter a small resistance called a shunt resistance is connected to its coil in parallel. To convert a galvanometer into a voltmeter a large resistance is connected in series with its coil.

What is the importance of Oersted's experiment?

Oersted's experiment indicates the presence of magnetic field in the surrounding region of a current carrying conductor. Oersted noticed that there is a deflection in magnetic compass needle kept near a straight current carrying wire. He found that the alignment of the needle is tangential to an imaginary circle which has the straight wire at its centre and has its plane perpendicular to the wire.The deflection in the needle changes with the amount of current and its direction and distance of the needle from the wire. Hence, it was concluded that the moving charges or currents produce magnetic field in the surrounding space.

E M B I B E

Intermediate Second Year Physics>Chapter 7 - Moving Charges and Magnetism>MODEL QUESTIONS (IPE PATTERN)>Q 7

HARD

12th Andhra Pradesh Board

IMPORTANT

Earn 100

Derive an expression for the magnetic dipole moment of a revolving electron.

Important Questions on Moving Charges and Magnetism

HARD

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 7 - Moving Charges and Magnetism>MODEL QUESTIONS (IPE PATTERN)>Q 8

Explain how crossed $\vec{E}$ and $\vec{B}$ fields serve as a velocity selector.

MEDIUM

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 7 - Moving Charges and Magnetism>MODEL QUESTIONS (IPE PATTERN)>Q 9

What are the basic components of a cyclotron? Mention its uses.

HARD

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 7 - Moving Charges and Magnetism>MODEL QUESTIONS (IPE PATTERN)>Q 1

Deduce an expression for the force on a current -carrying conductor placed in a magnetic field. Derive an expression for the force per unit length between two parallel current-carrying conductors.

HARD

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 7 - Moving Charges and Magnetism>MODEL QUESTIONS (IPE PATTERN)>Q 2

Obtain an expression for the torque on a current-carrying loop placed in a uniform magnetic field. Describe the construction and working of a moving coil galvanometer.

HARD

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 7 - Moving Charges and Magnetism>MODEL QUESTIONS (IPE PATTERN)>Q 3

How can a galvanometer be converted to an ammeter? Why is the parallel resistance smaller than the galvanometer resistance?

MEDIUM

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 7 - Moving Charges and Magnetism>MODEL QUESTIONS (IPE PATTERN)>Q 4

How can a galvanometer be converted to a voltmeter? Why is the series resistance greater than the galvanometer resistance?

HARD

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 7 - Moving Charges and Magnetism>MODEL QUESTIONS (IPE PATTERN)>Q 5

Derive an expression for the force acting between two very long parallel current carrying conductors and hence define the Ampere.

EASY

12th Andhra Pradesh Board

IMPORTANT

Intermediate Second Year Physics>Chapter 7 - Moving Charges and Magnetism>MODEL QUESTIONS (IPE PATTERN)>Q 1

A current of $10 A$ passes through two very long wires held parallel to each other and separated by a distance of $1 m$ . What is the force per unit length between them?

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