Tag: physics

Questions Related to physics

To protect iron from corrosion and rusting , it is electroplated with 

physics chemical effects of electric current applications of electrolysis electroplating extraction of metals by electrolysis

  1. Zinc

  2. Chromium

  3. Nickel

  4. Aluminum

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Correct Option: A
Explanation:

Iron is coated with a more active metal like Zinc. This is a sacrificial method. If the rusting conditions are met, zinc rusts before iron and prevents iron from rusting. Zinc makes a protective layer with Zn(OH)2 and ZnCO3

Electroplating does not help

physics chemical effects of electric current applications of electrolysis electroplating extraction of metals by electrolysis

  1. fine finish to the surface

  2. shining appearance

  3. metals to become hard

  4. protect metals against corrosion

Show answer
Correct Option: C
Explanation:

Electroplating is primarily used to change the surface properties of an object like appearance, corrosion protection, lubricity etc.  Thus, electroplating does not help in making the metals become hard. 

Chromiumhas a shiny appearance and lt does not corrode

physics chemical effects of electric current applications of electrolysis electroplating extraction of metals by electrolysis

  1. True

  2. False

  3. Ambiguous

  4. Data insufficient

Show answer
Correct Option: A
Explanation:

Answer is A.
Electroplating is a very useful process. It is widely used in industry for coating metal objects with a thin layer of a different metal. The layer of metal deposited has some desired property, which the metal of the object lacks. For example, chromium plating is done on many objects such as car parts, bath taps, kitchen gas burners, bicycle handlebars, wheel rims and many others.
Chromium has a shiny appearance. It does not corrode. It resists scratches. However, chromium is expensive and it may not be economical to make the whole object out of chromium. So the object is made from a cheaper metal and only a coating of chromium over it is deposited.
Hence, electroplating of chromium is done on objects like water taps and cycle bell to give them a shiny appearance and prevent them from corrosion. The statement is true.

In electroplating of silver spoon with gold ,silver spoon will act as :

physics chemical effects of electric current applications of electrolysis electroplating extraction of metals by electrolysis

  1. anode

  2. cathode

  3. positively charged electrode

  4. none of these

Show answer
Correct Option: B
Explanation:

The object on which we have to deposit a material, should always be at cathode

In electroplating of a silver spoon with gold,the gold plate is taken as:

physics chemical effects of electric current applications of electrolysis electroplating extraction of metals by electrolysis

  1. negatively charged electrode

  2. cathode

  3. anode

  4. All of the above

Show answer
Correct Option: C
Explanation:

The material which should be deposited on the object is always at anode.

In electroplating of the silver spoon with gold, the silver spoon is cleaned with a dilute acid solution to remove the  _________  from its surface.

physics chemical effects of electric current applications of electrolysis electroplating extraction of metals by electrolysis

  1. oxide layer

  2. chloride layer

  3. silver layer

  4. gold layer

Show answer
Correct Option: A
Explanation:

The silver spoon is cleaned with a dilute acid solution to remove the oxide layer from its surface and washed in running water until it is free from the acid.

Two capillaries of same length and radii in the ratio 1: 2 are.connected in series. A liquid flows through them in streamlined condition. If the pressure across the two extreme ends of the combination is 1 m of water, the pressure difference across first capillary is

physics pressure in fluids and atmospheric pressure pressure exerted by a liquid column pressure at a certain depth in liquid variation of pressure with depth

  1. 9.4 m

  2. 4.9 m

  3. 0.49 m

  4. 0.94 m

Show answer
Correct Option: D
Explanation:
Here, $l _1 = l _2 = 1m$ and $\displaystyle \frac{r _1}{r _2} = \frac{1}{2}$

As $V = \displaystyle \frac{ \pi P _1 r _1^4 }{8 \eta l} = \frac{ \pi P _2 r _2^4 }{8 \eta l}$ or $\displaystyle \frac{ P _1 }{P _2 } = \left( \frac{ r _2 }{ r _1} \right)^4 = 16$

$\therefore P _1 = 16 P _2$

Since, both tubes are connected in series, hence pressure difference across the combination is
$P = P _1 + P _2$ $\Rightarrow$  $\displaystyle 1 = P _1 + \frac{P _1}{16}$
or $\displaystyle P _1 = \frac{16}{17} = 0.94 m$

A capillary tube of radius $r$ is immersed in water and water rises to a height of $h$. Mass of water in the capillary tube is $5\times 10^{-3}kg$. The same capillary tube is now immersed in a liquid whose surface tension is $\sqrt{2}$ times the surface tension of water. The angle of contact between the capillary tube and this liquid is $45^o$. The mass of liquid which rises into the capillary tube now is (in kg):

physics pressure in fluids and atmospheric pressure pressure exerted by a liquid column pressure at a certain depth in liquid variation of pressure with depth

  1. $5\times 10^{-3}$

  2. $2.5\times 10^{-3}$

  3. $5\sqrt{2}\times 10^{-3}$

  4. $3.5\times 10^{-3}$

Show answer
Correct Option: A
Explanation:

Since the force on liquid is proportional to $Scos(\theta )$, in the latter case, force will be $\sqrt { 2 } cos(\dfrac { \pi  }{ 4 } )=1$ times the force in first case. Hence, since the same force is applied, mass of water rising in the tube will be same.

A liquid is allowed to flow in a tube of truncated cone shape. Identify correct statement from the following.

physics fluid pressure pressure exerted by a liquid column pressure at a certain depth in liquid variation of pressure with depth

  1. The speed is high at the wider end and low at the narrow end

  2. The speed is low at the wider end and high at the narrow end

  3. The speed is same at both ends in a stream line flow

  4. The liquid flows with uniform velocity in the tube

Show answer
Correct Option: B
Explanation:

For an incompressible liquid equation of continuity $ Av = constant$

or, $ A \propto \cfrac{1}{v}$
Therefore at the wider end speed will be low and at the narrow end speed will be hgih.

If a capillary tube is tilted to $45^{\circ}$ and $60^{\circ}$ from the vertical then the ratio of length $l _{1}$ and $l _{2}$ of liquid columns  in it will be -

physics fluid pressure pressure exerted by a liquid column pressure at a certain depth in liquid variation of pressure with depth

  1. $1: \sqrt{2}$

  2. $\sqrt{2}:1$

  3. 1:2

  4. 2:1

Show answer
Correct Option: A
Explanation:

The expression for the capillary rise in a tube is given by, 


H = $ \dfrac {2T cos \theta}{\rho gr} $


where $ \theta$ is the contact angle and not the angle of tilt.


Thus, for all parameters constant,


at $ 60^o $


$ l _1 = H cos 60^0 $ = H/2


At $ 45^o $


$ l _2 = H cos 45^0 $ = $ H/\sqrt 2 $


Therefore the ratio of the 2 lengths is given by,


$ l _1/l _2 = \dfrac {1}{\sqrt 2} $