Physics

Current Electricity and Circuits

377 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

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$%

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

A resistor is marked with the rings coloured brown, black, green and gold. The resistance in ohm is?

  1. $(3.5\times 10^5\pm 5\%)$
  2. $(1.10\times 10^5\pm 10\%)$
  3. $(8\times 10^6\pm 5\%)$
  4. $(1\times 10^6\pm 5\%)$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
By color coding
Brown Black Green Gold
$1             .0   \times10^6 \pm5\%$
Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

In a triode, $g$$ _m$ $= 2$ $\times$$ 10$$^{-3}$ $\Omega^{-1}$, $\mu$ $= 42$, resistance of load, $R = 50k\Omega$. The voltage amplification obtained from this triode will be

  1. $30.42$
  2. $29.57$
  3. $28.18$
  4. $27.15$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Voltage gain, $\displaystyle A _v = \beta \dfrac{R _L}{R _i} = 0.6 \times \dfrac{24}{3} = 4.8$

Multiple choice transistor and its types the bipolar junction transistor electronic devices semiconductor electronics: materials, devices and simple circuits physics

The grid voltage of any triode valve is changed from -1 volt to -3 volt and the mutual conductance is 3$\times$ 10$^{-4}$ mho. The change in plate circuit current will be

  1. 0.8 mA

  2. 0.6 mA

  3. 0.4 mA

  4. 1 mA
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\displaystyle g _m = \frac{\Delta I _p}{\Delta V _g}$

or $\Delta I _p = g _m \times \Delta V _g = 3 \times 10^{-4} \times [-3-(-1)]$
$= - 0.6 \times 10^{-3} A$ = shortage of $0.6 \times 10^{-3}A$

Multiple choice types of cells electricity physics

The power supplied by a battery (or source) is maximum when the external resistance 'R' is equal to the 

  1. Internal resistance 'r'

  2. Half of the internal resistance 'r'

  3. Two times of initial resistance 'r'

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

According to the Maximum Power Transfer Theorem, the power delivered to an external load is maximized when the load resistance equals the internal resistance of the source. This is derived by setting the derivative of power with respect to R to zero.

Multiple choice types of cells electricity physics

A cell of emf E is connected across a resistance r . The potential difference terminals of the cell is found to be V . The internal resistance of the cell must be 

  1. $\dfrac { \left( E-V \right) V }{ r } $
  2. $\dfrac { 2\left( E-V \right) V }{ r } $
  3. $\dfrac { \left( E-V \right) r }{ V } $
  4. $\left( E-V \right) r$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The terminal voltage V is given by V = E - Ir, where I = V/r_ext. Substituting I, we get V = E - (V/r_ext) * r_int. Rearranging for r_int gives r_int = (E - V) * r_ext / V. The provided options use 'r' as the external resistance.

Multiple choice types of cells electricity physics

A cell drives a current of 1 A in to load of resistance $4W$. On doubling the load resistance. the current is found to be reduced by $40 \%$. The internal resistance of the cell is

  1. $0.5 W$
  2. $1 W$
  3. $4 W$
  4. $2 W$
Reveal answer Fill a bubble to check yourself
A Correct answer
Multiple choice evs mud and stones soil types types of soil soil - types, uses and need for conservation

It rc and rs respectively represents cuticular and stomatal resistances, the total resistance (R) could be expressed as.

  1. $R=rc+rs$
  2. $R=r-rs$
  3. $\displaystyle\frac{1}{R}=\frac{1}{rc}+\frac{1}{rs}$
  4. $\displaystyle\frac{r}{R}=\frac{1}{rc}-\frac{1}{rc}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In plant physiology, resistances to water vapor diffusion (like cuticular and stomatal resistance) are arranged in series. Therefore, the total resistance R is the sum of the individual resistances: R = rc + rs.

Multiple choice maths percent and percentage use of percentages converting between fractions or decimals and percentages percentage of a quantity

The possible percentage error in computing the parallel resistance $R$ of three resistances $R _{1},R _{2},R _{3}$ from the formula $\dfrac {1}{R}=\dfrac {1}{R _{1}}+\dfrac {1}{R _{2}}+\dfrac {1}{R _{3}}$, if $R _{1},R _{2},R _{3}$ are each by $1.2\%$

  1. $1.2$
  2. $1.3$
  3. $1.3$
  4. $1.7$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

For parallel resistances, if each resistance has the same percentage error, the equivalent resistance inherits that same percentage error. With 1/R = 1/R₁ + 1/R₂ + 1/R₃, taking the differential shows that percentage error propagates directly when all resistances have identical % errors.