The magnetic field at the centre O of the following current loop is

(a)

\(\frac { { \mu }_{ ° }I }{ 4r } \bigotimes \)

(b)

 \(\frac { { \mu }_{ ° }I }{ 4r } \bigodot \)

(c)

\(\frac { { \mu }_{ ° }I }{ 2r } \bigotimes \)

(d)

\(\frac { { \mu }_{ ° }I }{ 2r } \bigodot \)

A particle having mass m and charge q accelerated through a potential difference V. Find the force experienced when it is kept under perpendicular magnetic field \(\vec { B } \).

(a)

\(\sqrt { \frac { 2{ q }^{ 3 }BV }{ m } } \)

(b)

\(\sqrt { \frac { { q }^{ 3 }{ B }^{ 2 }V }{ 2m } } \)

(c)

\(\sqrt { \frac { 2{ q }^{ 3 }{ B }^{ 2 }V }{ m } } \)

(d)

\(\sqrt { \frac { { 2q }^{ 3 }BV }{ { m }^{ 3 } } } \)

A thin insulated wire forms a plane spiral of N = 100 tight turns carrying a current I = 8 m A (milli ampere). The radii of inside and outside turns are a = 50 mm and b = 100 mm respectively. The magnetic induction at the centre of the spiral is ______.

(a)

\(5\mu T\)

(b)

\(7\mu T\)

(c)

\(8\mu T\)

(d)

\(10\mu T\)

A bar magnet of length l and magnetic moment p_m is bent in the form of an arc as shown in Figure. The new magnetic dipole moment will be

(a)

p_m

(b)

\(\frac{3}{\pi} p_{m}\)

(c)

\(\frac{2}{\pi} p_{m}\)

(d)

\(\frac{1}{2} p_{m}\)

The BH curve for a ferromagnetic material is shown in the figure. The material is placed inside a long solenoid which contains 1000 turns/cm. The current that should be passed in the solenoid to demagnetize the ferromagnet completely is _____.

(a)

1.00 m A

(b)

1.25 mA

(c)

1.50 mA

(d)

1.75 mA

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?

(a)

30° 

(b)

45° 

(c)

60° 

(d)

90° 

Which of the following graphs shows the variation of magnetic induction B with distance 'r' from along wire carrying current?

(a)

(b)

(c)

(d)

Which one of the following represents current magnetic field lines?

(a)

(b)

(c)

(d)

A current carrying conductor is associated with  _______________.

(a)

electric field

(b)

magnetic field

(c)

electro magnetic

(d)

all these

If a current I is flowing in a straight wire parallel to the x-axis and magnetic field is in the y-axis then the wire experiences in _________________.

(a)

in Z-direction

(b)

in Y- direction

(c)

no force

(d)

in X- diection

The unit of magnetic field is _______________.

(a)

ampere-turn

(b)

ampere

(c)

newton coulomb

(d)

tesla

A galvanometer coil has a resistance of 15Ω and gives full-scale deflection for a current of 4mA. To convert it to an ammeter of range 0 to 6 amp ____________.

(a)

10mΩ resistance is to be connected in parallel to the galvanometer

(b)

10mΩ resistance is to be connected in series with the galvanometer

(c)

0.1mΩ resistance is to be connected in series with the galvanometer

(d)

0.1mΩ resistance is to be connected in parallel to the galvanometer

Fuse wire is _____________.

(a)

an alloy of lead and copper

(b)

has low resistance

(c)

has high resistance

(d)

has high melting point

According to Joule's heating effect the law of resistance is _______________. 

(a)

H ∝ R

(b)

H ∝ R²

(c)

R ∝ H²

(d)

all the above

A 110 W, 220 V bulb draws a current _______________.

(a)

2 A

(b)

440 A

(c)

0.5 A

(d)

5.5 A

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

(a)

square and cube respectively of the current

(b)

square and the first power, respectively of the current

(c)

square of the current

(d)

current

Which one of the following pair of particles move with same velocity along the same circular path in a uniform magnetic field?

(a)

electron, proton

(b)

proton, deutron

(c)

proton, alpha particle

(d)

deutron, alpha particle

When the number of turns (n) in a galvanometer is doubled, current sensitivity __________________.

(a)

remains constant

(b)

decreases twice

(c)

increases twice

(d)

increases four times

Two T.G's having reduction factor K₁ and K₂ are connected series and give deflections θ₁and θ₂ respectively. Then K₁ : K₂ _____________________.

(a)

θ ₁ : θ ₂

(b)

tanθ₁ : tanθ₂

(c)

θ ₂ : θ ₁

(d)

tanθ₂ : tanθ₁

What is the current passing through a coil of radius of 8 cm having 50 turns, when a magnetic intensity at the centre of the coil is 125 A turns m^-1?

(a)

0.1 ampere

(b)

0.4 ampere

(c)

1 ampere

(d)

4 ampere