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When a magnetic compass needle is carried nearby to a straight wire carrying current, then
(i) the straight wire cause a noticeable deflection in the compass needle.
(ii) the alignment of the needle is tangential to an imaginary circle with straight wire as its centre and has a plane perpendicular to the wire
Both points are correct and these are the result of experiments done by Danish physicist Hans Christian Oersted in 1820.
Which one of the following is not correct about Lorentz force?
If charge is not moving then the magnetic force is zero.
Since
As for stationary charge ∴ .
A strong magnetic field is applied on a stationary electron. Then the electron
As
As the electron is stationary. ∴ velocity
∴ So, electron will remain stationary.
In an inertial frame of reference, the magnetic force on a moving charged partic le is Its value in another inertial frame of reference will be
which shows magnetic field is velocity dependent due to which it differs from one intertial frame to another.
The magnetic force on a current carrying conductor of length l in an external magnetic field is given by
A straight wire having mass of 1.2 kg and length of 1m carries a current of 5A. If the wire is suspended in midair by a uniform horizontal magnetic field, then the magnitude of field is
For midair suspension the upward force F on wire due to magnetic field B must be balanced by the force due to gravity, then
IIB = mg; B = mg/II
Here, m = 1.2 kg, g = 10 m s^{2}, l = 5 A, l = 1m
A circular loop of radius R carrying a current I is placed in a uniform magnetic field B perpendicular to the loop. The force on the loop is
A 2.5 m long straight wire having mass of 500 is suspended in mid air by a uniform horizontal magnetic field B. If a current of 4 A is passing through the wire then the magnitude of the field is (Take g = 10 m s^{2})
Here, m = 500g = 0.5kg, l = 4A, l = 2.5m
As F = IIB sinθ
mg = IIB sin90^{°}, (∵ θ= 90^{°}and F = mg)
A current of 10 A is flowing in a wire of length 1.5 m. A force of 15 N acts on it when it is placed in a uniform magnetic field of 2 T. The angle between the magnetic field and the direction of the current is
F = IlBsinθ or sinθ = F/IlB
or θ = 30^{°}
The horizontal component of earth's magnetic field at a certain place is 3.0 x 10^{5} T and having a direction from the geographic south to geographic north. The force per unit length on a very long straight conductor carrying a steady current of 1.2 A in east to west direction is
Force per unit length f = F/l = IB sinθ
when the current is flowing from east to west then θ = 90°, hence
f = IBsin 90° = 1.2 x 3 x 10^{5} x 1 = 3.6 x 10^{5 }N m^{1}.
A circular coil of 20 turns and 10 cm radius is placed in a uniform magnetic field of 1.10T normal to the plane of the coil. If the current in the coil is 5A, crosssectional area is 10^{5} m^{2} and coil is made up of copper wire having free electron density about 10^{29} m^{3}, then the average force on each electron in the coil due to magnetic field is
Force on each electron,
ev_{d}B = IB/nA
Here, I = 5 A, B = 0.1 T, n = 10^{29} m^{3},
A = 10^{5}m^{2}
So,
The magnetic force per unit length on a wire carrying a current of 10 A and making an angle of 45° with the direction of a uniform magnetic field of 0.20 T is
l = 10 A, θ = 45°, B = 0.2 T
∴ F = IlB sin θ
∴ F/l = IB sin 45^{°} = 10 x 0.2 x 1/√2 = 2/√2 N m^{1}
An 8 cm long wire carrying a current of 10 A is placed inside a solenoid perpendicular to its axis. If the magnetic field inside the solenoid is 0.3 T, then megnetic force on the wire is
F = lIB sinθ
Here, θ = 90^{0}, l = 10 A,
l = 8cm = 8 x 10^{2}m, B = 0.3T
F = 10 x 8 x 10^{2} x 0.3 x sin 90^{0} = 0.24 N
A rectangular coil ABCD is hung from one side of a balance as shown in figure. A 500 g mass is added to the other arm to balance the weight of the coil. A current of 9.8 A is passed through the coil and a constant magnetic field of 0.4 T acting inward (in xz plane) is switched on such that only arm CD of length 1.5 cm lies in the field. The additional mass m must be added to regain the balance is
In absence of magnetic field the weight added in one pan balances the rectangular coil in the other pan of balance,
∴ Mgl = W_{coil}l or W_{coil} = Mg = 0.5 x 9.8 N
When current I is passed through the coil and the magnetic field is switched on.
Let m mass be added in the first pan to regain the balance
Then Mgl + mgl = W_{coil }l + IBL sin90° l
mgl = IBLI
or
= 6 x 10^{3} kg = 6 g
Which one of the following is correct statement about magnetic forces?
As the action and reaction are instantaneous in III^{rd} law. But magnetic forces transmit with finite speed c.
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