Tag: electric power

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

A neon lamp is connected to a voltage a.c. source. The voltage is gradually increased from zero volt. It is observed that the neon flashes at $50 V$. The a.c, source is now replaced by a variable dc source and the experiment is repeated. The neon bulb will flash at ?

  1. $50V$
  2. $70V$
  3. $100V$
  4. $35V$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Answer is B.

The RMS (Root mean square) value tells us what equivalent DC voltage we would need to get the same power, for the neon bulb to glow.
In this case, the neon bulb glows at 50 V ac voltage. Therefore, for the bulb glow with dc voltage, $50\times \sqrt { 2 }  =50\times 1.414=70V$ dc voltage should be applied.
Hence, the neon bulb will flash at 70 V dc.

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

Two dissimilar bulbs are connected in series, which bulb will be brighter ?

  1. low resistance bulb

  2. more resistance bulb

  3. high current pass bulb.

  4. low current pass bulb
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Components connected in series are connected along a single path, so the same current flows through all of the components. The current through each of the components is the same, and the voltage across the circuit is the sum of the voltages across each component.
When two bulbs are connected in series the first bulb will receive more current. As the bulb has its own resistance, less current will flow to the next bulb.
Hence the first bulb will glow more.

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

The wire having a green plastic covering is a

  1. live wire.

  2. neutral wire.

  3. earth wire.

  4. none of these.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Black, Red and Blue are used for hot wires and White is used as the neutral wire in a 120/208 V circuit. Brown, Orange and Yellow are used as hot wires and gray is used as the neutral wire in a 277/480 V. For grounding, regardless of the voltage, Green is used.The wire having a green plastic covering is a earth wire.

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

An electrician not aware of the colour coding of resistors connected two resistors A and B in series to a 6V battery of internal resistance $3\Omega$ and an ammeter. The ammeter connected in the circuit was not working and hence he disconnected the ammeter from the circuit. The sequence of the colour bands on resistor. A is yellow, violet and brown while that on resistor B is red, violet and black respectively. By using the colour coding of resistors, help the electrician to determine the current flowing through the circuit. 

  1. $12$ mA
  2. $24$ mA
  3. $48$ mA
  4. $32$ mA
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given: resistors A and B connected in series to a $6V$ battery of $3\Omega$ internal resistance. The sequence of the colour bands on resistor. A is yellow, violet and brown while that on resistor B is red, violet and black respectively. 

To find the current flowing through the circuit.
Solution:
According to the question the A and B are 3-band resistors, so the thirdcode will be a multiplier.
And using the standard resistor color code table the value of:
yellow is 4, violet is 7, brown is $\times 10^1$, red is 2, black is $\times 10^0$.
The corresponding value of A and B are:
A= $47\times 10^1=470\Omega$, B= $27\times 10^0=27\Omega$
Now A and B are in series are also the internal resistance will also be in series. So the effective resistance of the circuit will be $R _{eq}=470+27+3=500\Omega$.
We know according to Ohm's Law,
$V=IR\implies I=\dfrac VR\\implies I=\dfrac 6{500}=0.012A$
Or the current flowing through the circuit = $12mA$

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

The wire having a red plastic covering is a

  1. live wire.

  2. neutral wire.

  3. earth wire.

  4. none of these.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The wire has a red plastic covering is a live wire. Red wire signifies the phase in an electric circuit. It is the live wire that cannot be connected to another red or bulb wire Red is used in some types of the switch leg.

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

The electricity tariff in a town is $Rs.3.00$ per unit. Calculate the cost of running an $80 W$ fan for $10 h$ a day for the month of June.

  1. $Rs. 12.00.$
  2. $Rs. 52.00.$
  3. $Rs. 72.00.$
  4. $Rs. 92.00.$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Total time for which the fan is used $= (10 hours) \times (30 days) = 300$ hours.
Energy consumed $= (80 W) \times (300$ hours$)$
$= 24,000 Wh = 24 kWh.$
But $1 kWh =1$ unit.
Therefore, $24 kWh = 24$ units
The cost of this power $= 24$ units $\times Rs. 3= Rs. 72.00.$

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

The wire having a black plastic covering is a

  1. live wire.

  2. neutral wire.

  3. earth wire.

  4. none of these.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Black, Red and Blue are used for hot wires and White is used as the neutral wire in a 120/208 V circuit. Brown, Orange and Yellow are used as hot wires and gray is used as the neutral wire in a 277/480 V. For grounding, regardless of the voltage, Green is used.The wire having a black plastic covering is a neutral wire.

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

The colour code of a resistor is brown, black and brown. Then the value of resistance is _____

  1. $10$ $\Omega$
  2. $100\ m \Omega$
  3. $0.1\ k$$\Omega$
  4. $1000$ $\Omega$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

First two colours says about significant digits of resistance and the third colour gives multiplier.


Brown colour gives digit $1$, brown colour gives digit $0$ and for multiplier brown colour gives $10^1$.

Hence, resistance  $=R=10\times 10^1=100\Omega$

$\implies R=0.1k\Omega$

Answer-(C)

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

An electric oven of 2 kW power rating is operated in a domestic electric circuit that has a current rating of 5A. If the supply voltage is 220V, what result do you expect?

  1. circuit will be breaked

  2. fuse will blow

  3. both

  4. none
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given,
Power of the oven $(P) = 2kw = 2 \times 103 W$
Voltage supplied $(V) = 220V$
Current $(I) = ? A$
Power $= V \times I$
$\Rightarrow I = P/V = 2 \times 103/220 = 9.09 A$
Since the domestic electric circuit has a current rating of 5A, the flow of 9.09 A by the Oven exceeds the safe limit. Here, fuse will blow and break the circuit.