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

Why is parallel arrangement used in domestic wiring?

  1. For getting same potential difference across each electrical appliance.

  2. For getting different potential difference across each electrical appliance.

  3. For getting high potential difference across each electrical appliance.

  4. For getting low potential difference across each electrical appliance.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The usage of parallel arrangement in domestic circuits has many advantages.

  • Each circuit will have the same potential difference which is equal to  the potential difference of the supply line. As a result, each electrical appliance will work under constant voltage.
  • When two or more appliances are used at the same time, each appliance will be able to draw the current as needed. The appliances having low resistance will draw higher current and vice versa.
  • When distribution circuits are in parallel, then each circuit operates separately. So, if one of the distribution circuits gets overloaded, only the fuse in that circuit will be blown off. The other distribution circuits will remain unaffected.

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

The most important safety method used for protecting home appliances from short circuiting or overloading is

  1. earthing.

  2. use of fuse.

  3. use of stabilizers.

  4. use of electric meter.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Answer is B

Fuses are safety devices that are to be built into our electrical system. If there were no fuses and we operated too many appliances on a single circuit, the cable carrying the power for that circuit would get extremely hot, short circuit, and possibly start a fire. To prevent electrical overloads, fuses are designed to trip or blow, stopping the flow of current to the overloaded cable.

Fuse is a piece of wire of a material with a very low melting point. When a high current flow through the circuit due to overloading or short circuit, the wires gets heated and melts. As a result, the circuit is broken and current stops flowing.

The fuse must always be connected to the mains and it must be of correct value. For example, a 15-ampere fuse should trip when the current through it exceeds 15 amperes. A 20-ampere fuse should blow when the current through it exceeds 20 amps.

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

The resistance of hot turngsten filament is about $10$ times the cold resistance. What will  be the resistance of $100W$ and $200V$ lamp when not in use

  1. $40\Omega $

  2. $20\Omega $

  3. $400\Omega $

  4. $200\Omega $
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given,

$P= 100W$
$V= 200V$
${ R } _{hot}= 10 \cdot { R } _{ cold }$
We know,
$ P= I \cdot V$
$ \rightarrow P= \cfrac{ V }{ R } \cdot { V }= { V }^{ 2 } \cdot R$
$ \therefore R= \cfrac{{ V }^{ 2 }}{P}$
where, 
$ P= $ Power
$ I = $ Current
$ R = $ Resistance
$ V =$ Voltage
$ { R } _{ hot }= $ Hot Resistance
${ R } _{ cold }=$ Cold Resistance
So, $ { R } _{ hot}= \cfrac {200 \cdot 200}{ 100}= 400 \Omega$
${ R } _{ cold }= \cfrac{{ R } _{ hot }}{ 10 }= \cfrac{ 400 }{ 10 }= 40 \Omega $
$\Rightarrow { R } _{ cold }= 40 \Omega$
$ 40 \Omega $ will be the resistance of $100W$ and $200V$ lamp when not in use.

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

The line that draws power supply to your house from Street has

  1. $220\sqrt{2}$ average voltage.

  2. 220 V average voltage

  3. voltage and current Out of phase by $\pi/2$

  4. voltage and current possibly differing in phase $\phi$ such that $| \phi| < \dfrac{\pi}{2}.$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

As the line has some resistance $(R \, \neq \, 0)$. Also, line that draws power supply has some inductance and capacitance, hence voltage and current differ in phase $\phi$ such that $|\phi| \, < \, \dfrac{\pi}{2}$.

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

Which arrangement is used for domestic circuits ?

  1. Series

  2. Parallel

  3. Series and parallel both

  4. None
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For Domestic circuits parallel arrangement is always used because:

  1. In parallel circuits, if one electrical appliance stop working due to some effect then all other appliances keep working normally.
  2. In parallel circuit, each electrical appliance has own switch due to which it can be turn off or on independently, without effecting  other appliances.
  3. In parallel circuits, each electrical appliance gets same voltage as that of the power supply line.
  4. In the parallel connection of electrical appliances, the overall resistance of the house hold circuit is reduced due to which the current from the power supply is high.

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

If the length of filament of a heater is reduced by  10%, the power of the heater will 

  1. increase by about 9%

  2. increase by about 11%

  3. increase by about 19%

  4. increase by about 10%
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$P=\dfrac { { V }^{ 2 } }{ R } \ R=\dfrac { \rho l }{ A } \ \therefore P=\dfrac { { V }^{ 2 }A }{ \rho l } $

$ \therefore P\alpha \dfrac { 1 }{ l } \quad $ [Keep in $\dfrac{v^2A}{\rho }$ constant]
$\therefore$ with reduction of $l$ by $10\%$ power will increase by $10\%$.

Multiple choice physics quantum physics photons concept of photon photons and photoelectric effect

The photoelectric cut off voltage in a certain experiment is 1.5 V. The maximum kinetic energy of photoelectrons emitted is then

  1. 2.4 eV

  2. 1.5 eV

  3. 3.1 eV

  4. 4.5 eV
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The minimum negative potential applied to the plate or anode  for which the photoelectric current just becomes zero, So, in this case, maximum K.E of an electron will be equal to stopping potential.
Here, $V _0 \, = \, 1.5 \, V,$
Maximum Kinetic energy = $eV _{0} \, = \, 1.5 \,eV$

Multiple choice physics quantum physics photons concept of photon photons and photoelectric effect

Light of wavelength 0.6 mm from a sodium lamp falls on a photocell and causes the emission of photoelectrons for which the stopping potential is 0.5 V. With light of wavelength 0.4 mm from a sodium lamp, the stopping potential is 1.5 V. With this data, the value of h/e is:

  1. $6\times {{10}^{-5}}\,V{{s}^{-1}} $

  2. $2\times {{10}^{-15}}\,V{{s}^{-1}} $

  3. $4\times {{10}^{-55}}\,V{{s}^{-1}} $

  4. $4\times {{10}^{-15}}\,V{{s}^{-1}} $

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In emission of electron, Potential Energy

$eV = \dfrac{hc}{\lambda} - W _0$

When light of wavelength $\lambda =0.6\,mm$and stopping potential $0.5\,V$
$0.5e=\dfrac{hc}{6\times {{10}^{-7}}}-{{W} _{0}}\ ......\ (1)$

When light of wavelength $\lambda =0.4\,mm$and stopping potential $1.5\,V$
$1.5e=\dfrac{hc}{4\times {{10}^{-7}}}-{{W} _{0}}\ ......\ (2)$
subtract equation (1) from (2) $ e=\dfrac{hc}{{{10}^{-7}}}\left[ \dfrac{1}{4}-\dfrac{1}{6} \right] $

$ \Rightarrow \dfrac{h}{e}=\dfrac{12\times {{10}^{-7}}}{3\times {{10}^{8}}}=4\times {{10}^{-15}}\,V{{s}^{-1}} $ 

Multiple choice physics quantum physics photons concept of photon photons and photoelectric effect

Photons absorbed in meter are converted to heat. A source emitting $n$ photons/s of frequency $v$ is used to convert $1\ kg$ of ice of ${0}^{o}c$ to water at ${0}^{o}C$. Then, the time taken for the conversion:

  1. decreases with increasing $n$, with $v$ fixed

  2. decreases with $n$ fixed, $v$ increasing

  3. remains constant with $n$ and $v$ changing such that $nv=$constant

  4. increases when the product $nv$ increases
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The energy absorbed per second is P = n * h * v. Since the energy required to melt the ice is constant, the time taken is inversely proportional to the power P. Thus, increasing n (with v fixed) increases power and decreases time.