Tag: electric current through conductors

Questions Related to electric current through conductors

Two cells, having the same e.m.f are connected in series through an external resistance R. Cells have internal resistance $r _1$ and $r _2$ ( $r _1$ > $r _2$) respectively. When the circuit is closed, the potential difference across the first cell is zero. the value of R is

physics electric current through conductors combination of resistors combination of cells combinations of components

  1. $\dfrac{r _1 + r _2}{2}$

  2. $\dfrac{r _1 - r _2}{2}$

  3. ${r _1 + r _2}$

  4. ${r _1 - r _2}$

Show answer
Correct Option: D
Explanation:
Two cells of emf E are connected in series through external resistance R.
Thus, total resistance is R + r1 + r2
 
Thus, current across the circuit is total voltage divided by total resistance.
I=E+E/R+r1+r2
I=2E/R+r1+r2
 
Now, when circuit is closed, the voltage across first cell is zero. Thus, we have
Ir1=E
E/r1=2E/R+r1+r2
R=r1-r2
This is the value of R in terms of r1 and r2.

Which of the following statement(s) is/are correct?

physics electric current through conductors combination of resistors combination of cells combinations of components

  1. If n identical cells are connected in series and then the battery thus formed is short circuited by a conduction wire, current through the wire will be independent of n.

  2. If n identical cells are connected in parallel and then the battery thus formed is short circuited by a conducting wire, current through the wire will be directly proportional to n.

  3. If n identical cells are connected in parallel and then the battery thus formed is short circuited by a wire having a constant resistance, current through the wire will be directly increase as n increases.

  4. None of the above.

Show answer
Correct Option: A,B
Explanation:

In series, $I=\frac{nE}{nr}=\frac{E}{r}$ (i.e., I is 
independent of n)

In parallel, $I=\frac{E}{r/n}=\frac{nE}{r}, i.e,.\frac{nE}{r}, 
i.e.I\propto n$

After shorting by a wire having a constant resistance 
$I=E\left (R+\frac{r}{n}  \right )$

A battery of 20 cells (each having e.m.f. 1.8 volt and internal resistance 0.1 ohm) is charged by 220 volts and the charging current is 15A. The resistance to be put in the circuit is

physics electric current through conductors combination of resistors combination of cells combinations of components

  1. 10.27 ohms

  2. 12.27 ohms

  3. 8.62 ohms

  4. 16.24 ohms

Show answer
Correct Option: A
Explanation:

The total emf of the 20 cells connected in series are $1.8\times 20=36 V$. 

Hence, the total voltage in the circuit is $220V - 36V  =  184 V.$
From the Ohm's law, $V=IR$. Substituting the values of Voltage and current in the equation

 $R=\dfrac { V }{ I } ,\quad we\quad get\quad R=\dfrac { 184 }{ 15 } =12.27\quad ohms$.

The internal resistance of the 20 cells is given as  $20\times 0.1ohms=2 ohms$.
So, the total resistance R in the circuit is $ =12.27-2 ohms = 10.27 ohms.$
Hence, the resistance in the circuit is 10.27 ohms.

Which resistor is difficult to make of having a value less than about 2 Ohms? 

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

  1. Iron Resistor

  2. Carbon Resistor

  3. Wire wound Resistor

  4. Both b and c

Show answer
Correct Option: B
Explanation:

Carbon resistor is difficult to make of having a value less than about $20 $Ohms because they have ability to withstand high energy pulses, when current flow through the carbon composition body conducts the energy . So carbon resistor can be made with a higher resistance 

Resistors are generally colour coded to:

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

  1. Indicate the type of the circuit in which they are to be used

  2. Identify whether they are ohmic or non-ohmic

  3. Determine their values in ohm

  4. Determine whether they are wire wound or composition resistors

Show answer
Correct Option: C
Explanation:

Components and wires are coded with colors to identify their value and function. The colors brown, red, green, blue, and violet are used as tolerance codes on 5-band resistors only.

So,Resistors are generally colour coded to determine their values in ohm.
Therefore, C is correct option.

Which of the following is not true for wire wound resistor?

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

  1. It has a lower order of stability and reliability.

  2. It has high power rating with a low tolerance value.

  3. Easy to make wire wound resistor of value 0.01 Ohm.

  4. It is not suitable for high-frequency circuits.

Show answer
Correct Option: A
Explanation:
A wire wound resistor is an electrical passive component that limits current. The resistive element exists out of an insulated metallic wire that is winded around a core of non-conductive material. The wire material has a high resistivity, and is usually made of an alloy such as Nickel-chromium (Nichrome) or a copper-nickel-manganese alloy called Manganin. Common core materials include ceramic, plastic and glass. 
It has a lower order of stability and reliability  is not true for wire wound resistor

A given resistor has the following colour scheme of the various strips on it : Brown, black, green and silver. Its value in ohm is :

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

  1. $1.0 \times 10^4 \pm 10\%$

  2. $1.0 \times 10^5 \pm 10\%$

  3. $1.0 \times 10^6 \pm 10\%$

  4. $1.0 \times 10^7 \pm 10\%$

Show answer
Correct Option: B
Explanation:

Numbers attached for brown, black, green and silver are $1, 0, 5, \pm10\%$. Therefore the resistance of given resistor
$= 10 \times 10^5\  \Omega  \pm 10\%$.

Which of the following is not the disadvantage of wire wound resistor?

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

  1. It has a big size which is not suitable for many of the applications.

  2. It has high power rating with a low tolerance value.

  3. Resistance value gets changed by a change in temperature, humidity etc.

  4. It is not suitable for high-frequency circuits.

Show answer
Correct Option: C
Explanation:

In wired resistors are mainly produced with alloys, since pure metal has a high temperature co-efficient.

Due to alloy temperature co-efficient of wire wound resistor is very low.
Therefore it is very less effected by temperature change.

There are three red colored bands on a carbon resistor. What is its resistance ?

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

  1. $2.2$

  2. $2200$

  3. $\left( 2200\pm 20\% \right) $

  4. $1.76$ to $2.64$

Show answer
Correct Option: C
Explanation:

According to the color code of resistance,

code of red $=2$
code of red $=2$
code of red $=2$
The resistance of carbon resistor, $22\times 10^2 \pm20$%
$2200\pm20$%
The correct option is C.

Which color band  in the color coding of a resistor has the tolerance $\pm2$%?

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

  1. Orange

  2. Black

  3. Silver

  4. Red

Show answer
Correct Option: D
Explanation:

Red color band in the color coding of a resistor has the tolerance of $\pm2\%$