Tag: physics

Questions Related to physics

The null point should be obtained on the meter bridge wire to get maximum accuracy at

physics current electricity meter bridge meter bridge and problems on it galvanometer

  1. the middle of the wire.

  2. the left end of the wire.

  3. the right end of the wire.

  4. the 1/4th distance from the left end.

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Correct Option: A
Explanation:

The null point, when obtained at the middle of wire, will give us maximum accuracy as the resistance on both the side will be equal.

In specific resistance measurement of a wire using a meter bridge, the key k in the main circuit is kept open when we are not taking readings. The reason is

physics current electricity meter bridge meter bridge and problems on it galvanometer

  1. the emf of cell will decrease.

  2. the value of resistance will change due to joule heating effect.

  3. the galvanometer will stop working.

  4. none of these.

Show answer
Correct Option: B
Explanation:
The key k in the main circuit is kept open when we are not taking the readings because the value of resistance will change due to joule heating effect. When an electric current passes through the resistor, heat is generated which rises the temperature of resistor which in result changes the resistance of resistor.

In a Wheatstone bridge, three resistances P, Q and R are connected in the three arms and the fourth arm is formed by two resistances $S _1$ and $S _2$ connected in parallel. The condition for the bridge to be balanced will be

physics current electricity meter bridge meter bridge and problems on it galvanometer

  1. $\displaystyle \frac{P}{Q} = \frac{R(S _1 + S _2)}{2S _1S _2}$

  2. $\displaystyle \frac{P}{Q} = \frac{R}{S _1 + S _2}$

  3. $\displaystyle \frac{P}{Q} = \frac{2R}{S _1 + S _2}$

  4. $\displaystyle \frac{P}{Q} = \frac{R(S _1 + S _2)}{S _1S _2}$

Show answer
Correct Option: D
Explanation:

The balanced condition for Wheatstone bridge is  $\dfrac{P}{Q}=\dfrac{R}{S}$

Here $S=\frac{S _1S _2}{S _1+S _2}$  (as $S _1$ and $S _2$ are connected in parallel in S arm)
so, $\dfrac{P}{Q}=\dfrac{R(S _1+S _2)}{S _1S _2}$

Mark the correct set of ferromagnetic substances,

physics magnetism and matter magnetic materials behaviour of substances in magnetic field classification of magnetic materials

  1. iron, cobalt and nickel

  2. iron, copper and lead

  3. silicon, bismuth and nickel

  4. aluminium, sodium and copper.

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Correct Option: A
Explanation:

Iron, cobalt and nickel are the examples of ferromagnetic material.

Nickel shows ferromagnetic property at room temperature. If the temperature is increased beyond Curie temperature, then it will show the

physics magnetism and matter magnetic materials behaviour of substances in magnetic field classification of magnetic materials

  1. anti ferromagnetism

  2. no magnetic property

  3. diamagnetism

  4. paramagnetism

Show answer
Correct Option: D
Explanation:

Above Curie temperature, ferromagnetic material become paramagnetic.

Assertion : When diamagnetic material is placed in a non-uniform magnetic field, it tends to move from stronger to the weaker part of the magnetic field.
Reason : Diamagnetic materials possess strong magnetism.

physics magnetism and matter magnetic materials behaviour of substances in magnetic field classification of magnetic materials

  1. If both assertion and reason are true and reason is the correct explanation of assertion.

  2. If both assertion and reason are true and reason is not the correct explanation of assertion.

  3. If assertion is true but reason is false.

  4. If both assertion and reason are false.

Show answer
Correct Option: C
Explanation:

Electrons is an atom orbiting around nucleus possess orbital angular momentum. These orbiting electrons are equivalent to current-carrying loop and thus possess orbital magnetic moment. Diamagnetic substances are the ones in which resultant magnetic moment in an atom is zero. When magnetic field is applied, those electrons having orbital magnetic moment in the same direction slow down and those in the opposite direction speed up. Thus, the substance develops a net magnetic moment in direction opposite to that of the applied field.

Assertion : At high temperature, a ferromagnet becomes a paramagnet.
Reason : The ferromagnetic property depends on temperature.

physics magnetism and matter magnetic materials behaviour of substances in magnetic field classification of magnetic materials

  1. If both assertion and reason are true and reason is the correct explanation of assertion.

  2. If both assertion and reason are true and reason is not the correct explanation of assertion.

  3. If assertion is true but reason is false.

  4. If both assertion and reason are false.

Show answer
Correct Option: A
Explanation:

At enough high temperature, a ferromagnet become a paramagnet. The domain structure disintegrates with temperature.

Assertion : The product of magnetic susceptibility and absolute temperature for a paramagnetic substance is constant.
Reason : Susceptibility is positive but very small for paramagnetic substance.

physics magnetism and matter magnetic materials behaviour of substances in magnetic field classification of magnetic materials

  1. If both assertion and reason are true and reason is the correct explanation of assertion.

  2. If both assertion and reason are true and reason is not the correct explanation of assertion.

  3. If assertion is true but reason is false.

  4. If both assertion and reason are false

Show answer
Correct Option: B
Explanation:

The susceptibility of a paramagnetic substance is inversely proportional to absolute temperature.
$X \propto \frac{1}{T}$
Hence $XT = constant$
Also for paramagnetic substances the susceptibility is positive and very small.

If a magnetic material is having magnetic susceptibility $(\chi)=-1$, then the relative magnetic permeability $(\mu _r)$ and type of magnetic material is?

physics magnetism and matter magnetic materials behaviour of substances in magnetic field classification of magnetic materials

  1. $0$, diamagnetic

  2. $2$, ferromagnetic

  3. $1$, paramagnetic

  4. $-1$, diamagnetic

Show answer
Correct Option: A
Explanation:

Here, $\chi =-1$
then $\mu _r=1+\chi \Rightarrow \mu _r=1+(-1)=I-1=0$
Since, magnetic susceptibility of given material is less than one. Hence, the given magnetic material is a diamagnetic material.

A domain in ferromagnetic iron is in the form of a cube of side length $2$ $\mu m$ then the number of iron atoms in the domain are (Molecular mass of iron $=55$g $mol^{-1}$ and density $=7.92$g $cm^{-3}$)

physics magnetism and matter magnetic materials behaviour of substances in magnetic field classification of magnetic materials

  1. $6.92\times 10^{12}$ atoms

  2. $6.92\times 10^{11}$ atoms

  3. $6.92\times 10^{10}$ atoms

  4. $6.92\times 10^{13}$ atoms

Show answer
Correct Option: B
Explanation:

The volume of the cubic domain
$V=(2\mu m)^3=(2\times 10^{-6}m)^3$
$=8\times 10^{-18}m^3=8\times 10^{-12}cm^3$
and mass $=$volume $\times$ density
$=8\times 10^{-12}cm^3\times 7.9g cm^{-3}$
$=63.2\times 10^{-12}$g
Now the Avagadro number $(6.023\times 10^{23})$ of iron atoms have a mass of $55$g. Hence the number of atoms in the domain are.
$N=\dfrac{63.2\times 10^{-12}\times 6.023\times 10^{23}}{55}=6.92\times 10^{11}$ atoms.