Tag: domestic electric circuits and safety precautions

Questions Related to domestic electric circuits and safety precautions

A house hold $20$ liter geyser consist of a coil of resistance $R$, across which an $ac$ source of $rms$ voltage $V$ is connected. The wall thickness of geyser is $t(< < \sqrt{A})$ and the inner surface area of geyser is $A$. The average thermal conductivity of material of walls of geysers is $k$ and $S$ is specific heat capacity of water. Assuming initial temperature of water is equal to the temperature of atmosphere. The time taken to rise the temperature of water by $50^{o}C$ is (Neglect the specific heat of wall of geyser and radiation losses)

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. $\dfrac{2St}{kA} In \left(\dfrac{50RkA}{rV^{2}}-1\right)$

  2. $\dfrac{20St}{kA} In \left(\dfrac{tV^{2}}{V^{2}t-20RkA}-1\right)$

  3. $\dfrac{20St}{kA} In \left(\dfrac{50tV^{2}}{RkA}\right)$

  4. $\dfrac{20St}{kA} In \left(\dfrac{50RkA}{tV^{2}}\right)$

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Correct Option: A

The voltage of domestic ac is $220\ V$. What does this represent?

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. Mean voltage

  2. Peak voltage

  3. Root mean voltage

  4. Root mean square voltage

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Correct Option: C

If 2.2 kW power transmits 22000 V in a line of $10 \Omega$ resistance, the value of power loss will be :-

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. 0.1 W

  2. 10 W

  3. 100 W

  4. 1000 W

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Correct Option: A

Mircrowave oven acts on the principle of 

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. Giving rotational energy to water

  2. Giving translational energy to water molecular

  3. Giving vibrational energy to water molecules

  4. None of these

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Correct Option: D
Explanation:

Microwave oven act on the principle of transferring electron from lower 

to higher energy level in water molecule.

Four wires made of same material have different lengths- and radii, the wire having more resistance in the following case is 

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. $l= 100 cm, r= 1 mm$

  2. $l= 50 cm, r= 2 mm$

  3. $ l= 100 cm, r=\frac { 1}{2} mm $

  4. $ l= 50 cm, r=\frac { 1}{2} mm $

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Correct Option: C

A bulb made of tungsten filament of surface area $0.5 c{ m }^{ 2 }$ is heated to a temperature 3000 k when operated at 220 V. The emissivity of the filament is $ \in =0.35$ and take $\sigma =5.7\times 1{ 0 }^{ -8 }$ mks units. Then the wattage of the bulb is .. (calculate)

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. 80.8 W

  2. 0.81 W

  3. 81.2 W

  4. 8.12 W

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Correct Option: A

What is the frequency of 220$\mathrm { v } \mathrm { DC }$ voltage? 

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. Zero HZ

  2. 50$\mathrm { Hz }$

  3. 60$\mathrm { Hz }$

  4. 220$\mathrm { Hz }$

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Correct Option: A

How the small bulbs, which are used for decoration purpose,are connected?

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. in parallel

  2. in series

  3. in mixed order

  4. all of the above

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Correct Option: B
Explanation:

Bulbs used for decoration purposes are connected end to end, that is, in series. This ensures that same amount of current flows through them and the voltage divides across the bulbs as required for low voltage operation. Thus when one bulb goes out, due to being in series, all the bulbs stop glowing.

Which of the following appliances is not of lower power rating ?

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. Tubelight O

  2. TV O

  3. Fan O

  4. Geyser O

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Correct Option: D

A student in town in India, where the price per unit ($1 unit = 1 kW-hr$) of electricity is $Rs.5.00$, purchases a $1 kVA$ UPS (uninterrupted power supply) battery. A day before the exam, 10 friends arrive to the student's home with their laptops and all connect their laptops to the UPS. Assume that each laptop has a constant power requirement of $90 W$. Consider the following statements :


I. All the 10 laptops can be powered by the UPS if connected directly.
II. All the 10 laptops can be powered if connected using an extension box with a $3 A$ fuse.
III. If all the 10 friends use the laptop for 5 hours, then the cost of the consumed electricity is about $Rs.22.50.$

Select the correct option with the true statements.

physics electrical circuits domestic electric circuits and safety precautions domestic and commercial circuit electric power

  1. I only

  2. I and II only

  3. I and III only

  4. II and III only

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Correct Option: C
Explanation:
power supplied by battery $1\ kVA=1000\ W$

$1$ laptop required $90\ W$.

and all $10$ laptop are connected directly so,

$P _T=90\ W\times 10=900\ W$

$1\ unit=1\ KW\ hr$ cost $=5\ Rs$.

So, If $10$ Laptops are used for $5\ hr$ well consumed

$unit=\dfrac{900\times 5\times 3600}{3600000}=4.5$

Total pay amount in $5\ hr=4.5\ unit\times 5$
                         $=22.5\ rupees$