Tag: physics

Questions Related to physics

State whether true or false.
Opaque objects allow light to pass through them.

physics light and shadow substances which allow light to pass through and those which do not transparent, opaque and translucent objects shadows

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

Transparent objects allow the light to pass through them whereas opaque objects doesn't allow any light ray to pass through them.

State whether true or false:
You can clearly see through a blue-tinted drinking glass.

physics light and shadow substances which allow light to pass through and those which do not transparent, opaque and translucent objects shadows

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

No since the dispersion of light occurs when we observe things through the blue tinted drinking glass so objects are not so clear.

State whether true or false:
Wood is an example of opaque object.

physics light and shadow substances which allow light to pass through and those which do not transparent, opaque and translucent objects shadows

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

Since opaque object are objects which doesn't allow any light ray to pass through it and we cannot see through it. For example wood.

In ........................... lens, all the rays diverge after refraction.

physics light and shadow substances which allow light to pass through and those which do not transparent, opaque and translucent objects shadows

  1. Concave

  2. Bi-concave

  3. Convex

  4. Bi-convex

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Correct Option: A

An object is transparent if you can see through it clearly.

physics light and shadow substances which allow light to pass through and those which do not transparent, opaque and translucent objects shadows

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

A transparent substance is defined as the substance through which all light incident on it normally can pass through it.And hence , it can be seen clearly through a transparent substance.


Given statement is $True$.

A two kilowatt motor pumps out water from a well 10 meter deep. The quantity of water pumped out per hour  is ( g = 10 $m/s^2$)

physics work and power commercial unit of energy power work and energy

  1. $72 \times 10^2$ kg

  2. $72 \times 10^3$ kg

  3. $72 \times 10^4$ kg

  4. $72 \times 10^5$ kg

Show answer
Correct Option: B
Explanation:

Two kilowatt motor  pump means that 2kJ wotk is done in $1$ sec 

Let $m$ be the mass of water that is pumped out 
Work done , $W=2\ kJ=2000\ J$
Time taken , $t=1 sec$

Displacement of water , $h= 10\ m$

As in this case  $W=mgh $

$\implies 2000= m\times 10\times 10$
$\implies m=20\ kg$

Quantity of water pumped out per sec , $m=20\ kg$

$\therefore \text{ Quantity of water that is pumped out per hour }= m\times 3600=20\times 3600= 72\times 10^3 \ kg $

If the heart pushes 1 cc of blood in one second under pressure 20000 $N/m^2$ the power of heart is:

physics work and power commercial unit of energy power work and energy

  1. 0.02 W

  2. 400 W

  3. 20 mW

  4. 0.2 W

Show answer
Correct Option: A
Explanation:

Given that , 
Pressure ,$P=2000 N/m^2$
Change in Volume = $1 cc= 10^{-6 } L $

$\text{Power}=\dfrac{\text{workdone}}{\text{time}}=\dfrac{\text{pressure }\times \text{ change in volume}}{\text{time}}=\dfrac {2000\times 10^{-6}}{1}= 0.02 \ W$

The pump of a water pumping system uses $2.0\ kW$ of electrical power when raising water. The
pumping system lifts $16kg$ of water per second through a vertical height of $7.0\ m$.
What is the efficiency of the pumping system?

physics work and power commercial unit of energy power work and energy

  1. $1.8\%$

  2. $5.6\%$

  3. $22\%$

  4. $55\%$

Show answer
Correct Option: B
Explanation:

The power of pump = $\dfrac{d(mgh)}{dt}$

                                 = $(16 \times 10 \times 7 ) W$
                                  = $112 W$
So, efficiency = $\dfrac{P _{out}}{P _{in}}\times 100$
                       = $\dfrac{112}{2000} \times 100$
                       =  $5.6 %$%

Choose the correct option.

physics work and energy commercial unit of energy power work and power

  1. kW$=$ unit of power and kWh $=$ unit of energy.

  2. kW$=$ unit of energy and kWh $=$ unit of power.

  3. kW and kWh are both of unit of energy.

  4. kW and kWh are both of unit of power.

Show answer
Correct Option: A
Explanation:

Electrical Power is measured in watts (W), kilo-watts (kW), mega-watts (MW), and giga-watts (GW). The power of a load can change quickly, especially if the load is turning on and off.

Electrical Energy is measured in kilowatt-hours (kWh), megawatt-hours, and sometimes (less commonly) in watt-hours or watt-seconds. Energy is the primary measurement used by the utility company to determine your bill each month (although demand and power factor are also sometimes used). Unlike power, energy does not change quickly, but instead accumulates gradually.

In our household applications, commercial unit of electricity is used. One unit is equal to:

physics work and energy commercial unit of energy power work and power

  1. $1\ kW$

  2. $1\ kWh$

  3. $1\ kW/h$

  4. $1\ Wh$

Show answer
Correct Option: B
Explanation:

Electrical Energy is measured in kilowatt-hours (kWh). A unit is the primary measurement used by the utility company to determine your bill each month (although demand and power factor are also sometimes used). Unlike power, energy does not change quickly, but instead accumulates gradually.