Physics

Power, Energy, and Efficiency

443 Questions

Power, energy, and efficiency are fundamental physics concepts that quantify work and the rate of doing work. Questions cover electrical energy consumption in kilowatt hours, the efficiency of thermodynamic cycles like the Brayton cycle, and mechanical power lifting loads. This topic is essential for general science and engineering exam preparation.

Electrical energy consumptionBrayton cycle efficiencyPower calculation formulasCommercial electricity unitsHydraulic lift mechanics

Power, Energy, and Efficiency Questions

Multiple choice physics option b: engineering physics conversion of heat into work: heat engine and it's efficiency engines and cycles refrigerators and heat pumps

A 1 h.p. electric motor operates a pump continuously. The work performed by the motor in one day is

  1. 18 kWh

  2. 36 kWh

  3. 54 kWh

  4. 72 kWh
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

1 h.p. is approximately 0.746 kW. In one day (24 hours), the work performed is 0.746 kW * 24 h = 17.904 kWh, which rounds to 18 kWh.

Multiple choice

1000 ml of D5W over 8 hours. Flow rate?

  1. 100 gtts/min

  2. 125 ml/hr

  3. 60 gtts/ml

  4. 100 ml/hr
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

To find the flow rate in ml/hr, divide the total volume by the total time. 1000 ml / 8 hours = 125 ml/hr.

Multiple choice physics electric current and its effects electric fuse electrical fuse and mcb fuse

An electric iron draws a current of 15 A from a 220 V supply. What is the cost of using iron for 30 min everyday for 15 days if the cost of unit (1 unit $=$ 1 k W hr) is 2 rupees?

  1. Rs. 49.5

  2. Rs. 60

  3. Rs. 40

  4. Rs. 10
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$I=15 A, V=220 V, t=30 min$
$Energy=P\times t=VIt$
$=220\times 15\times \frac {30}{60}\times 15$
$=3300\times \frac {1}{2}\times 15 W hr$
$=3.3\times kW\times 7.5 hr$
$=24.75 kW hr$
$Cost=24.75\times 2=Rs. 49.50$

Multiple choice stefan's law black body radiation heat transfer thermal properties physics

The value of solar constant is approximately  :

  1. $ 1340\ watt/m^{2}$
  2. $ 430\ watt/m^{2}$
  3. $ 340\ watt/m^{2}$
  4. $ 1388\ watt/m^{2}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The solar constant is defined as the amount of heat energy received per second per unit area by a perfect black body placed at the surface of the Earth with its surface being held perpendicular to the direction of the sun's rays.

The value of solar constant is $1388$($\dfrac{watt}{{meter}^{2}}$) or $2$($\dfrac{cal}{{cm}{\times} {min}}$)

Multiple choice stefan's law black body radiation heat transfer thermal properties physics

What is the value of solar constant if the energy received by $ 12$ m$^2$ area in $2$ minutes is $2016$ kJ?

  1. $1.4 \times 10^2 J s^{-1} m^{-2}$
  2. $1400 J s^{-1}m^{-2}$
  3. $84 kJ s^{-1} m^{-2}$
  4. $84 J s^{-1} m^{-2}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
Solar constant = Energy received by unit area in unit time from Sun
$=\cfrac{2016\times 10^3}{12\times (2\times 60)} \\=1400Js^{-1}m^2$
Multiple choice stefan's law black body radiation heat transfer thermal properties physics

The solar energy incident on the roof in 1 hour of dimension $ 8m \times 20m$ will be

  1. $5.76\times { 10 }^{ 8 }J$
  2. $5.76\times { 10 }^{ 7 }J$
  3. $5.76\times { 10 }^{ 6 }J$
  4. $5.76\times { 10 }^{ 5 }J$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Here the power per unit area is given, $I=10^3  W/m^2$

So, the total power $=I\times $ area of roof $=10^3\times (8\times 20)=1.6\times 10^5 W$ 
Since power is the energy divided by time so, energy, $E=Pt=1.6\times 10^5 \times (3600)=5.76\times 10^8  J$

Multiple choice zoology energy flow in an ecosystem the energy pyramid ecological pyramid ecological pyramids

If the energy produced at the level of producers is 1000 J, the energy available for the secondary consumers is

  1. 1000 J

  2. 100 J

  3. 10 J

  4. 1 J
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In a food chain, only 10% of energy is transferred from one trophic level to another trophic level. If the energy produced at the producer level is 1000 J, then the energy available at the primary consumer level will be 100 J and energy available at the secondary consumer level will be 10 J.

Thus, the correct answer is '10 J'.

Multiple choice

What was the capacity of the Hubble Space Telescope's batteries?

  1. 20 ampere-hours

  2. 40 ampere-hours

  3. 60 ampere-hours

  4. 80 ampere-hours
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The Hubble Space Telescope's batteries had a capacity of 60 ampere-hours, which was enough to power the telescope's instruments and systems for up to 6 hours.

Multiple choice

What is the potential global capacity of tidal power?

  1. 100 GW

  2. 1,000 GW

  3. 10,000 GW

  4. 100,000 GW
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The potential global capacity of tidal power is estimated to be around 100,000 GW, which is significantly higher than the current global electricity demand.

Multiple choice

What was the energy released in the GW170817 event?

  1. 10^47 joules

  2. 10^50 joules

  3. 10^53 joules

  4. 10^56 joules
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The energy released in the GW170817 event was about 10^53 joules.