Physics

Current Electricity and Circuits

450 Questions

Current electricity and circuits questions cover resistors, EMF, internal resistance, and power calculations in series and parallel configurations. Solving these builds a strong understanding of electrical principles and circuit analysis. These physics problems are highly relevant for technical and science aptitude tests.

Resistor combinationsPower dissipationEMF and internal resistanceAC circuit analysisOperational amplifiers

Current Electricity and Circuits Questions

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

In the 5 band color resistor,which color bands are considered as significant digits?

  1. First band only

  2. First three bands

  3. First two bands

  4. Last band
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

A 5-bandcolor resistor is represented as

$R=abc\times d\pm e\%$
Where, $a$ represents the $1^{st}$ significant digit, which is the first band color of resistor.
$b$ represents the $2^{nd}$ significant digit, which is the second band color of resistor.
$c$ represents the $3^{rd}$ significant digit, which is the third band color of resistor.
$d$ represents the $4^{th}$ significant digit, which is the fourth band color of resistor and this is the multiplier value used in formula.
$e$ represents the $5^{th}$ significant digit, which is the fifth band color of resistor and this is the tolerance value of resistor.

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

According to international convention of colour coding in a wire

  1. Live is red, neutral is yellow and earth is green

  2. Live is red, neutral is green and earth is black

  3. Live is brown, neutral is blue and earth is black

  4. Live is red, neutral is black and earth is green
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

According to international color coding system in Old colors red is live ( or phase) black is neutral, green/ yellow is earth 
and in New colors brown is live, blue is neutral and green/ yellow is earth.

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

The power factor of a circuit in which a box having unknown electrical devices connected in series with a resistor of resistance $3\Omega$ is $3/5$. The reactance of the box is

  1. $5\Omega$
  2. $\dfrac{5}{3}\Omega$
  3. $4\Omega$
  4. $\dfrac{4}{3}\Omega$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The power factor is given by cos(theta) = R / Z = 3/5. Since resistance R = 3 ohms, the total impedance Z must be 5 ohms. Using the impedance formula Z = sqrt(R^2 + X^2), we get 5 = sqrt(3^2 + X^2), which yields a reactance X of 4 ohms.

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

Which of the following is true for carbon resistors?

  1. Resistance value does not get changed by change in temperature
  2. Current carrying capacity and hence power wattage are limited to about $50$ Watts.

  3. It has low-temperature coefficient value.

  4. Stability and reliability are very good.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$A\rightarrow$ Resistance value of carbon resistor with change in temperature it has negative thermal coefficient.

$B\rightarrow$ Carbon resistors are not current carrying capacitor.
$C\rightarrow$ Carbon has low temperature coefficient value i.e. higher the temperature, lower the resistivity.
$D\rightarrow$ Because of low stability of resistance value this type of resistors are not suitable.

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

Red,orange,black are the color bands on resistors.Find its resistance?

  1. $23\Omega \pm20$ %
  2. $25\Omega \pm10$ %
  3. $32\Omega \pm20$ %
  4. $53\Omega \pm15$ %
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For first two significant digits of resistance ,  we see the first two colours .

And, third color signifies the multiplier.

Here, red color means digit $2$ and orange color means $3$.
And for multiplier, black colour means multiplier of $1$.

Hence resistance is $(23\times 1)=23\Omega$

Since , nothing is said about fourth color, we can check answer from the calculated resistance.

Answer-(A)

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

Brown,black and gold is the color band on the resistor,find its resistance?

  1. $10\times 10^{-2}\Omega$
  2. $1\Omega$
  3. $100 \Omega$
  4. $10\times 10^{0}\Omega$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The first two colours are brown and black.


For first two significant digits we need to consider digits signified by first two colours.
And, brown colour signifies $1$, and black colour signifies $0$.
And for multiplier the third colour is considered which is here gold meaning $0.1$.

Hence, resistor is $10\times 0.1=1\Omega$

Answer-(B)

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

A carbon resistance with color band is $200\Omega$. If red band is replaced by green band then the new resistance is:

  1. $500\Omega$
  2. $300\Omega$
  3. $400\Omega$
  4. $100\Omega$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Significant figure of red band is $2$ and for green is $5$
 so new resistance $500 \Omega$

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

The carbon resistor has three orange bands. The maximum value of resistance offered by the resistor will be __________.

  1. $39.6k\Omega $
  2. $49.6k\Omega $
  3. $33k\Omega $
  4. $26.4k\Omega $
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
The resistance can be calculated with a help of the colour coding chart.
The colour of the first band indicates the first significant figure, the colour of the second band indicates the second significant figure and the colour of the third band indicates the multiplier to be used. 
Thus, the resistance of a carbon resistor with three orange bands would be:
3 (orange) 3(orange) x 1000 (orange) = 33,000 ohms

The maximum value of resistance $=33\times { 10 }^{ 3 }\Omega =33k\Omega $

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

Brown, Red and Orange coloured bands on a Carbon resistor are followed by silver band. The value of resistor is ________

  1. $320\Omega \pm 5$%
  2. $12k\Omega \pm 5$%
  3. $320\Omega \pm 10$%
  4. $12k\Omega \pm 10$%
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The Color Coding of the resistances is given by:


Black     Bown     Red     Orange    Yellow      Green     Blue     Violet     Grey     White
     0           1            2           3              4              5             6            7           8              9

Tolerance:
Gold     Silver     No color
    5%        10%         20%

So, according to the color-coding, 
$R=AB\times10^C \pm D$

Here, A is the first color, B is the second color, C is the third color and D is the strip of the tolerance.

So $R=12\times 10^3\pm10\%$

$\implies12k\Omega\pm10\%$

So option $D$ is correct.

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

Blue,green,yellow and yellow is the color band on the resistor,find its resistance?

  1. $(75\times 10^4 )\Omega \pm 5$%
  2. $(65\times 10^4 )\Omega \pm 5$%
  3. $(52\times 10^4 )\Omega \pm 5$%
  4. $(65\times 10^4 )\Omega \pm 10$%
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The first two colours are blue and green.


For first two significant digits we need to consider digits signified by first two colours.
And, blue colour signifies $6$, and green colour signifies $5$.
And for multiplier the third colour is considered which is here yellow meaning $10^4$.

And, for tolerance , fourth colour is given yellow meaning $5\%$.

Hence resistance is $ (65\times 10^4)\Omega \pm5\%$

Answer-(B)

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

The order of coloured rings in a carbon resistor is red, yellow, blue and silver. The resistance of the carbon resistor is :

  1. $24\times 10^6\ \Omega \pm 5\%$
  2. $24\times 10^6\ \Omega \pm 10\%$
  3. $34\times 10^4\ \Omega \pm 10\%$
  4. $26\times 10^4\ \Omega \pm 5\%$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

According to colour code of carbon resistors, red stands for $2$, yellow for $4$, blue for $6$ and silver stands for $5$%.
First and second band represents the first two significant figure of resistance.
Third band represents the power raised to $10$ in the value of resistance.
Fourth band represents the tolerance.
Thus resistance of given carbon resistor is  $24\times 10^{6} \ \Omega$
Tolerance in the resistance is $10%$.
Thus resistance is  $24\times 10^6 \Omega  \ \pm 10$%

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

A resistance of 600$\Omega$ has the color code given by 3 steps. The color of strips (from left to right) is given by

  1. blue, black & brown

  2. blue, brown & black

  3. brown, blue & black

  4. brown, black & blue
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Resistor Band Colors

As shown above, a carbon-composition resistor can have 4 to 6 bands. A 5-band resistor is more precise compared to a 4-band type because of the inclusion of a third significant digit. A 6-band resistor is like a 5-band resistor but includes a temperature coefficient band (the 6th band). 

|   | 4-band | 5-band | 6-band | | --- | --- | --- | --- | | 1st band | 1st significant digit | 1st significant digit | 1st significant digit | | 2nd band | 2nd significant digit | 2nd significant digit | 2nd significant digit | | 3rd band | multiplier | 3rd significant digit | 3rd significant digit | | 4th band | tolerance | multiplier | multiplier | | 5th band | N/A | tolerance | tolerance | | 6th band | N/A | N/A | temperature coefficient |

Each color represents a number if it's located from the 1st to 2nd band for a 4-band type or 1st to 3rd band for a 5-band and 6-band type. 

| Color | Value | | --- | --- | | Black (2nd and 3rd bands only) | 0 | | Brown | 1 | | Red | 2 | | Orange | 3 | | Yellow | 4 | | Green | 5 | | Blue | 6 | | Violet | 7 | | Grey | 8 | | White | 9 |

 

Mnemonics were created to easily memorize the sequence of the colors. The most popular mnemonic is "Big Boys Race Our Young Girls But Violet Generally Wins" where the first letter of each word corresponds to the first letter of the color. 

If the color is found on the 3rd band for a 4-band type or the 4th band for a 5-band and 6-band type, then it's a multiplier.

| Color | Value | | --- | --- | | Black | x1 | | Brown | x10 | | Red | x100 | | Orange | x1000 | | Yellow | x10000 | | Green | x100000 | | Blue | x1000000 | | Violet | x10000000 | | Grey | x100000000 | | White | x1000000000 |

Notice that the number of zeroes is equal to the color's number as per the previous table.

The fourth band (or 5th for the 5-band and 6-band) indicates the tolerance values. Here, two colors are added (gold and silver).

| Color | Value | | --- | --- | | Black | N/A | | Brown | ±1% | | Red | ±2% | | Orange | ±3% | | Yellow | ±4% | | Green | ±0.5% | | Blue | ±0.25% | | Violet | ±0.10% | | Grey | ±0.05% | | White | N/A | | Gold | ±5% | | Silver | ±10% |

The 6th band for a 6-band type resistor is the temperature coefficient. This indicates how much the actual resistance value of the resistor changes when the temperature changes.

| Color | Value | | --- | --- | | Black | N/A | | Brown | 100 ppm/ºC | | Red | 50 ppm/ºC | | Orange | 15 ppm/ºC | | Yellow | 25 ppm/ºC | | Green | N/A | | Blue | 10 ppm/ºC | | Violet | 5 ppm/ºC | | Grey | N/A | | White | N/A |

 

Color Code Exceptions

5 Band Resistor with a 4th Band of Gold or Silver

Five band resistors with a fourth band of silver or gold form an exception, and are utilized on specific or older resistors. The first two bands represent the significant digits, the third band is a multiplication factor, the fourth band is for tolerance and the fifth band is for the temperature coefficient (ppm/K).

Multiple choice physics electric current through conductors carbon resistance and colour codes for carbon resistance carbon resistors and their colour coding resistors

The colour code of a carbon resistor is, Brown, Black, Brown and Red. The value of the resistor is?

  1. $10\Omega \pm 5\%$
  2. $1k\Omega \pm 2\%$
  3. $100\Omega \pm 2\%$
  4. $10\Omega \pm 2\%$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to the colour code, brown colour stands for $1$, black for $0$ and red for  $2$.
First and second band represents the first and second significant number respectively.
So, it is  $10\Omega$.
Third band represents power of $10$ by which it is raised, so it is  $10^1$.
Last band represents the tolerance of resistor, so it is  $2$%.
Thus value of resistance,   $R = (10\times 10^1)\Omega \pm 2$% $ = 100\Omega \pm 2$%