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## Saturday, July 5, 2014

### Edugain HOTS Questions with Answer CBSE Chapter Magnetic Effects of Electric Currents

HOTS Questions with Answer:  Magnetic Effects of Electric Currents

Q1.On what factors does the magnetic field intensity at the centre of the circular coil carrying current  depend ?
Answer: The magnetic field intensity at the centre of the circular coil is directly proportional to current and inversely proportional to radius of the coil. So, in both the cases ,that is, twice the current as well as half in radius, the magnetic field intensity gets doubled.

The magnitude of the magnetic field (B) at the of the coil is:
(i). directly proportional to the current (I) flowing it.
i.e.   B α I                           ①
(ii). Inversely proportional to the radius (r) of the coil
i.e.  B α 1/r                              ②
From ①, and , we get

B α I/r

Q2.State the principle used to determine the force experienced by a conductor carrying current in uniform magnetic field ?

Answer: .Fleming’s Left Hand Rule-Stretch the first three fingers of the left hand mutually perpendicular to each other such that the fore finger points in the direction of magnetic field, the middle finger points in the direction of current, then the thumb will indicate the direction of force experienced by the conductor.
Q3.On what factors does the force experienced by a conductor carrying current in uniform magnetic field depend?
Answer: .Force experienced by a conductor depends on
(a)Current and
(b)The perpendicular distance between that point and the conductor.
(c)Magnetic field strength

Q4.On what factors does the strength of a magnetic field at a point due to a straight conductor carrying current depend ?
Answer:.(a)Magnitude of electric current and
(b)perpendicular distance between that point and the . Conductor.
The magnitude of the magnetic field (B) at the of the coil is:
(i). directly proportional to the current (I) flowing it.
i.e.   B α I                           ①
(ii). Inversely proportional to the radius (r) of the coil
i.e.  B α 1/r                              ②
(iii). directly proportional to total number of turns (N) in the coil.
i.e. B α N                              ③
From ①, ② and ③, we get

B α I x N/r

Q5.Differentiate between direct current and alternating current.
 Direct current In direct current (a)It has constant a) It varies in magnitude. (b)It has constant b) It changes its direction alternatively (c)It is less dangerous in terms of terms of shock. c) It is more dangerous in eclectic shock.

Q6.A switch is always connected in
(a)earth wire         (b)neutral wire                   (c)live wire

Answer: . It is always connected with live wire.

Q7.What type of connection is used in household circuits?
Answer: .In household circuits all electrical appliances are connected in parallel.

Q8.State the principle of the working of an electric motor.
Answer: .An electric motor works on the principle of force experienced by a current carrying conductor in a magnetic field. The two forces acting are equal and opposite. Since they act in different lines the bring rotational motion.

Q9.State the principle of a D.C generator.
Answer: .It is based on the principle of electromagnetic induction.

Q10.State the characteristics of magnetic field lines.
Magnetic field
The space surrounding a magnet in which magnetic force is exerted is called a magnetic field.
The magnetic field has both magnitude as well as direction.

The S.I.Unit of magnetic field is Newton/Ampere-meter. It is also called Tesla and is denoted by T.
1T=1Newton1ampere x1meter
So, 1T=1 N/Am

The magnetic field (B)of earth near its surface = 0.3 x 10-4T.

(i)The direction of magnetic field is indicated by the arrow in the line at any point (tangent).
(ii)The field lines come out of the north pole and emerge into the south pole(closed loops are formed).
(iii)No two field lines will never ever intersect each other.

Q11.State Right Hand Thumb Rule.
Answer: .Hold the wire carrying current in your hand, such that the thumb points in the direction of current, the direction of the curled fingers will indicate the the direction of magnetic field.

Answer: .If the total current drawn by all the appliances at a particular time exeeds the bearing capacity of that wire, the wires of the domestic wiring get heated.This Phenomenon is called overloading.

Q.13. How can it be shown that magnetic field exist around a wire carrying current?
Answer: By using magnetic compass which, shows deflection.
A current-carrying straight conductor is placed in the east-west direction. What

Q.14 Will be the direction of the force experienced by this conductor due to earth’s magnetic field? How will this force get affected on? (a) reversing the direction of flow of current (b) doubling the magnitude of current. The direction of earth’s magnetic field is from G-south to G-north.
Answer: Let current is from west to east. Therefore force is vertically upwards.
(a) By reversing the direction of current, the direction of will be reversed i.e. vertically downwards.
(b) The magnitude of the force is doubled.

Q.15. A wire carrying current passes through the middle of the plane A perpendicular to it. If a magnetic needle is placed in the plane parallel to the wire. What will be the direction of the needle?
Answer: (i) along the tangent to a circle going anti-clockwise to an out coming current( to plane A).

Q.16.A wire carrying current passes through the middle of the plane A perpendicular to it. If a magnetic needle is placed in the plane perpendicular to the plane A, what will be the direction of the needle? Answer: .Any direction, as the needle is not influenced by a perpendicular field.

Q.17.If a magnetic needle is placed at the north pole in a horizontal plane, in what direction it will indicate? Why?
Answer: They will show random orientation as the magnetic field at the poles are along the vertical line and not on the horizontal plane.

Q.18.If a magnetic needle is placed at the north pole in a vertical plane, what will be its direction?
Answer: .They will stand vertically.

Q.19. Is a circular coil carrying current similar to magnet?

Q.20. What is the role of soft iron in the core of a solenoid?
Answer: It acts as an electromagnet.

Q.21. What are the factor on which the magnitude of the magnetic field (B) inside the solenoid depends on?

Answer: The magnitude of the magnetic field (B) inside the solenoid is:

(i). directly proportional to the to the current flowing through it.
i.e.     B α I                           ①
(ii). directly proportional to the number of turns per unit length of the solenoid(n).
i.e.      B  α n                         ②
From ① and ②, we get
B α nI
Where n = N/l.
Here, N = Total number of turns in the solenoid
And   l = Length of solenoid.

Q. 22. What are the factor on which force acting on a current-carrying conductor placed in a magnetic field.

Answer: Magnitude of Force:- It has been found experimentally that the force (F) is:

(i). directly proportional to the current (I).

i.e. F∝ I ①

(ii). directly proportional to the length of the conductor inside the magnetic field.

i.e. F ∝ L ②

(iii). directly proportional to the magnitude of the magnetic field.

i.e. F α B ③

From ①, ② and ③, we get

F∝ ILB Or F=K x I x L xB

Q.23. What is magnetic flux?

Answer: The total number of lines of magnetic force in a material is called magnetic flux, f . The strength of the flux is determined by the number of magnetic domains that are aligned within a material. The total flux is simply the flux density applied over an area. Flux carries the unit of a weber, which is simply a tesla- meter2.

The number of magnetic lines of force cutting through a plane of a given area at a right angle is known as the magnetic flux density, B. The flux density or magnetic induction has the tesla as its unit. One tesla is equal to 1 Newton/(A/m). From these units, it can be seen that the flux density is a measure of the force applied to a particle by the magnetic field. The Gauss is the CGS unit for flux density and is commonly used by US industry. One gauss represents one line of flux passing through one square centimeter of air oriented 90 degrees to the flux flow.