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12th Physics weekly Test - 3 ( Magnetism and magnetic effects of electric current )

St. Britto Hr. Sec. School - Madurai

12th Physics weekly Test - 3 ( Magnetism and magnetic effects of electric current )-Aug 2020

Time : 1.00 Hours

Part - A

Multiple Choice Question - Answer All Question

The deflection in a galvanometer falls from 50 to 20 divisions when 12Ω shunt is applied. The galvanometer resistance is

18Ω
36Ω
24Ω
30Ω

The period of revolution of a charged particle inside a cyclotron does not depend on

the magnetic induction
the charge of the particle
the velocity of the particle
the mass of the particle

Above the neutral temperature the thermo emf

changes sign
is constant
increases with the rise in temperature
decrease with the rise in temperature

The deflection in moving coil galvanometer is reduced to half when it is shunted with a 40Ω coil. The resistance of the galvanometer is

60Ω
10Ω
40Ω
20Ω

Which one of the following has positive Thomson effect

Zn
Bi
Ni
Hg

The current through a solenoid of length 0.5 m with 400 turns produces a magnetic field 10^-3 tesla. The current is _______

2A
20
1A
0.5 mA

In which one of the following heating effect to current is undesirable?

electric iron
electric motor
fuse wire
electric bulb

Joule's heating effect and Peltier effect are proportional to the

square and cube respectively of the current
square and the first power, respectively of the current
square of the current
current

Which of the following principle is used in a thermopile?

Thomson effect
Peltier effect
Seebeck effect
Joules effect

Which one of the following represents corrent magnetic field lines?

Th ree wires of equal lengths are bent in the form of loops. One of the loops is circle, another is a semi-circle and the third one is a square. Th ey are placed in a uniform magnetic fi eld and same electric current is passed through them. Which of the following loop confi guration will experience greater torque ?

circle
semi-circle
square
all of them

1 water = ______

10⁶ maxwell
10⁷ maxwell
10⁸ maxwell
10⁵ maxwell

A moving coil galvanometershows a deflection of 12⁰, when a current of 1mA flows through it. If the current is 2 mA, then the deflection will be _____

10°
12°
14°
24°

The vertical component of Earth’s magnetic field at a place is equal to the horizontal component. What is the value of angle of dip at this place?

30°
45°
60°
90°

An α-particle enters a magnetic field of 1T with a velocity 10⁶ m/s in a direction perpendicular to the field. The force on α-particle is

1.6 x 10^-13N
6.4 x 10^-13N
4.8 x 10^-13N
3.2 x 10^-13N

The most suitable metal for permanent magnet is

copper
aluminium
steel
iron

The magnetic induction at the center of a circular coil having 5 turn and radius 2π cm carrying a current of 50 mA is

2π x 10^-7 T
50π x 10^-7 T
25π x 10^-7 T
2.5π x 10^-7 T

Two short bar magnets have magnetic moments 1.20 Am² and 1.00 Am² respectively. They are kept on a horizontal table parallel to each other with their north poles pointing towards the south. They have a common magnetic equator and are separated by a distance of 20.0 cm. The value of the resultant horizontal magnetic induction at the mid-point O of the line joining their centers is (Horizontal components of Earth’s magnetic induction is 3.6 x 10^-5 Wb m^-2 )

3.60 × 10^-5 Wb m^-2
3.5 × 10^-5 Wb m^-2
2.56 × 10^-4 Wb m^-2
2.2 × 10^-4 Wb m^-2

Consider the motion of a charged particle in a uniform magnetic field directed into the paper. If velocity v of the particle is in the plane of the paper, the charged particle will describe a

straight line
circle
ellipse
hyperbola

The ratio of magnetic length and Geometrical length is _______

\(\frac { 4 }{ 5 } \)
\(\frac { 5 }{ 6 } \)
\(\frac { 6 }{ 5 }\)
\(\frac { 5 }{ 4 } \)

If the temperature of hot junction is increased beyond inversion temperature the thermo emf

is constant
increases
decreases
becomes zero

The elements having Thomson positive effect are ________

Sb, Hg, Zn
Ag, Hg, Cd
Zn, Cd, Sb
Cd, Pt, Ag

A flat dielectric disc of radius R carries an excess charge on its surface. The surface charge density is σ. The disc rotates about an axis perpendicular to its plane passing through the center with angular velocity ω. Find the magnitude of the torque on the disc if it is placed in a uniform magnetic field whose strength is B which is directed perpendicular to the axis of rotation

\(\frac { 1 }{ 4 } \sigma \omega \pi BR\)
\(\frac { 1 }{ 4 } \sigma \omega \pi B{ R }^{ 2 }\)
\(\frac { 1 }{ 4 } \sigma \omega \pi B{ R }^{ 3 }\)
\(\frac { 1 }{ 4 } \sigma \omega \pi B{ R }^{ 4 }\)

The value of Bohr magneton is

9.27 x 10^-34 Am²
9.72 x 10^-34 Am²
9.27 x 10^-24 Am²
9.72 10^-24 Am²

A thermo-couple is formed by Mn and Hg. The current flows ______

from Mn to Hg at cold junction
from Hg to Mn at cold junction
from Hg to Mn at hot junction
when Mn and Hg are at same temperature

Thomson effect for _______ is zero.

Ag
Pt
Au
Pb

To convert a galvanometer into an ammeter we connect which one of the following to the galvanometer?

a low resistance in series
a high resistance in series
a low resistance in parallel
a high resistance in parallel

A wire of length l carries a current I along the Y direction and magnetic field is given by \(\vec { B } =\frac { \beta }{ \sqrt { 3 } } =(\hat { i } +\hat { j } +\hat { k } )T.\) The magnitude of Lorentz force acting on the wire is

\(\sqrt { \frac { 2 }{ \sqrt { 3 } } } \beta Il\)
\(\sqrt { \frac { 1 }{ \sqrt { 3 } } } \beta Il\)
\(\sqrt { 2 } \beta Il\)
\(\sqrt { \frac { 1 }{ 2 } } \beta Il\)

A long struight conductor carrying a current lies along the axis of a ring. The conductor will exert a force on the ring if

carries a current
has uniformly distributed charge
has non-uniformly distributed
none of the above

An ammeter of resistance of 0.8 Ω can measure current upto 2A. What must be the shunt resistance to enable the ammeter to measure currents up to 10A?

0.1 Ω
0.2 Ω
0.3 Ω
0.4 Ω

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