Tag: physics

Questions Related to physics

With a potentiometer null points were obtained at $140cm$ and $180cm$ for cells of emf $1.1V$ and one unknown $X$ volt. UNknown emf is: 

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

  1. $1.1V$

  2. $1.8V$

  3. $2.4V$

  4. $1.41V$

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Correct Option: D

The length of a potentiometer wire is $l$ A cell of emf E is balanced at a length $\dfrac{l }{ 3}$ from the positive end of the wire. If the length of the wire is increased by $\dfrac{l} { 2}$.
At what distance will the same cell give a balance point?

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

  1. $

    \dfrac{2l}{3}

    $

  2. $

    \dfrac{l}{2}

    $

  3. $

    \dfrac{l}{6}

    $

  4. $

    \dfrac{4l}{3}

    $

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Correct Option: B

In Wheatstone's bridge $  P=9  $ ohm, $  Q=11  $ ohm, $  R=4  $ ohm and $  S=6  $ ohm. How much resistance must be put in parallel to the resistance $  S  $ to balance the bridge

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

  1. $24 ohm$

  2. $ \frac{44}{9} ohm$

  3. $26.4 \mathrm{ohm} $

  4. $18.7 ohm$

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Correct Option: C

In metre bridge experiment, with a standard resistance in the right gap and a resistance coil dipped in water (in a beaker) in the left gap, the balancing length obtained is 'l'. If the temperature of water is increased, the new balancing length is

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

  1. >l

  2. none

  3. =0

  4. =l

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Correct Option: A
Explanation:

$\begin{array}{l} \frac { { { R _{ unknown } } } }{ { { R _{ s\tan  dard } } } } =\frac { l }{ { \left( { 1-l } \right)  } } . \ If\, \, temperature\, \, increases,\, \, resis\tan  ce\, \, increases. \end{array}$

Hence, Option $A$ is correct.

An electron is released from the origin at a place where a uniform electric field $\overrightarrow{E}$ and uniform magnetic field $\overrightarrow{B}$ exit along the negative y-axis and the negative z-axis respectively.

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

  1. At time $t$ the y-component of velocity of the electron becomes $u _y = \dfrac{E}{B}\sin \omega t$ where $\omega = \dfrac{eB}{m}$.

  2. At $t = \pi m / eB$ the electron will have only x-component of velocity.

  3. At $t = \dfrac{2\pi m}{3eB}$, the y-component of velocity becomes zero.

  4. The displacement along y-axis is $\dfrac{2Em}{eB^2}$ when the velocity of electron becomes perpendicular to the y-axis

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Correct Option: A,B

Two wires of resistances X and Y are connected in left and a right gap respectively of a slide wire bridge of length 170cm. The null point is obtained at the center of the wire. Now, the wire X is given a shape of a ring and two diametrically opposite points are connected in the left gap. The wire Y is stretched to double of its original length and is connected in the right gap. Find the shift in the null point:

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

  1. 75 cm

  2. 10 cm

  3. 126 cm

  4. Zero

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Correct Option: A

Which of the following statements is/are incorrect for a meter bridge, which is used to compare two resistances?

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

  1. If its wire is replaced by another wire having same length, made of same material but having twice the cross sectional area, the accuracy increases.

  2. If its wire is replaced by another wire of different material, having same cross sectional area but of twice the length, accuracy increases.

  3. If its wire is replaced by another wire of same material, having half the cross sectional radius and half the length, accuracy decreases but sensitivity increases

  4. Metre bridge works on the principle of Wheat-stone bridge.

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Correct Option: A
Explanation:

The Meter Bridge works on the principle of Wheatstone bridge. The accuracy would depend on the fact that how precisely we find out the balance length. As we find the balancing length manually , the accuracy would increase if the voltage variation along the length decreases so that the balancing length is larger and the relative uncertainty associated to it is less. Changing the area won't affect the accuracy much. However, it certainly would affect the sensitivity of meter bridge.

In measuring a resistant using metre bridge, the resistance in the gaps are interchanged to minimize error due to

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

  1. the yielding of the supports

  2. nonuniformity of the bridge wire

  3. the contact or end resistance

  4. Joule heating of the bridge wire.

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Correct Option: B

If the wire in the experiment to determine the resistivity of a material using metre bridge is replaced by copper or hollow wire the balance point i.e. null point shifts

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

  1. to right

  2. to left

  3. at same point

  4. None of these

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Correct Option: C
Explanation:

The null point will remain at same point because null point depends on known resistance, $R$ and unknown resistance , $S$ only. 
Null condition: $\dfrac{R}{S}=\dfrac{l}{100-l}$ where $l=$ null point position in the wire. 

In the experiment of half deflection method the resistance R should be

physics effects of electric current meter bridge meter bridge and problems on it galvanometer

  1. > S

  2. $\approx$ S

  3. < S

  4. $\approx$ G

Show answer
Correct Option: A
Explanation:

In half deflection method, Rg = (R)*(S)/(R-S) .
Here , Rg= Galvanometer resistance, R = high resistance in series with the galvanometer, S = low resistance in parallel with the galvanometer. We want to approximate Rg in terms of S which we are able to vary in the experiment . If R>>S then Rg = S.