Tag: charging and discharging

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Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

The filament of an electric bulb is made of :

  1. Carbon

  2. Aluminium

  3. Tungsten

  4. Nickel
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The filament of an electric bulb is made of tungsten because it has some amazing properties including the highest melting point $(3422^oC )$, lowest vapor pressure, and greatest tensile strength out of all the metals. Because of these It can reach high temperature before melting.  

Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

Like charges .......... and unlike charges.................

  1. Repel, Attract

  2. Attract, Repel

  3. Always attract

  4. Always repel
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

There are two types of charges, positive and negative. Same type of charges (two positive or two negative) repel each other, while unlike charges (one positive and one negative) attract each other.

Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

An insulated conductor initially free from charge is charged by repeated contacts with a plate which after each contact is replenished to a charge $Q$ from an electrophorus. If $q$ is the charge on the conductor after the first operation,  The maximum charge which can be given to the conductor in this way is $Qq/(Q - q)$.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

This is a geometric series problem where the charge on the conductor after n operations is q_n = q(1 + (q/Q) + (q/Q)^2 + ... + (q/Q)^(n-1)). As n approaches infinity, this converges to q / (1 - q/Q) = Qq / (Q - q).

Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

 A point charge Q is placed at origin O. Let $\overrightarrow {{E _A}} $,$\overrightarrow {{E _B}} $ and $\overrightarrow {{E _C}} $ represent electric fields at A, B and C respectively. If coordination of A,B and C are respectively (1,2,3) m,(1,1,-1) m and (2,2,2) m  then 

  1. $\overrightarrow {{E _A}} \bot \overrightarrow {{E _B}} $

  2. $\overrightarrow {{E _A}} \parallel \overrightarrow {{E _B}} $

  3. $\left| {\overrightarrow {{E _B}} } \right|\parallel 4\left| {\overrightarrow {{E _C}} } \right|$

  4. $\left| {\overrightarrow {{E _B}} } \right|\parallel 8\left| {\overrightarrow {{E _C}} } \right|$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$\overrightarrow{E _a}=\cfrac{h _E}{ra^3}=\cfrac{h _E}{1^2+2^2+3^2}(1\hat{i}+2\hat{j}+3\hat{k})\ \overrightarrow{E _a}=\cfrac{h _E}{14^{3/2}}(1\hat{i}+2\hat{j}+3\hat{k})\ \overrightarrow{E _b}=\cfrac{ha}{r _b^2}\overrightarrow{r _b}=\cfrac{h _E}{(1^2+1^2+1^2)}^{3/2}(1\hat{i}-1\hat{j}+1\hat{k})\=\cfrac{h _E}{3^{3/2}}(1\hat{i}-1\hat{j}+1\hat{k})\ \overrightarrow{E _c}=\cfrac{h _E}{r _c^2}\overrightarrow{r _c}=\cfrac{h _E}{(2^2+2^2+2^2)^{3/2}}(2\hat{i}+2\hat{j}+2\hat{k})$

$\quad=\cfrac{h _E}{12^{3/2}}(2\hat{i}+2\hat{j}+2\hat{k})$
Now 
$\overrightarrow{E _a}.\overrightarrow{E _b}=\cfrac{h _E}{14^{3/2}}(1\hat{i}+2\hat{j}+3\hat{k})=\cfrac{h _E}{3^{3/2}}(1\hat{i}-1\hat{j}+1\hat{k})\ \Rightarrow \overrightarrow{E _a}.\overrightarrow{E _b}=(\cfrac{h _E}{14^{3/2}})(\cfrac{h _E}{3^{3/2}})(1-2+3)\neq0$
Thus$\overrightarrow{E _a}$ and $\overrightarrow{E _b}$ are perpendicular to each other
$|E _c|=\cfrac{h _E}{12^{3/2}}(2^2+2^2+2^2)^{1/2}=\cfrac{h _E}{12^{3/2}}(12)^{1/2}\ \Rightarrow |\overrightarrow{E _c}|=\cfrac{h _E}{12}\ \overrightarrow|E _b|=\cfrac{ha}{3^{3/2}}(1^2+1^2+1^2)^{1/2}=\cfrac{ _E}{3}=4\times\cfrac{h _E}{12}=4|\overrightarrow{E _c}|$
So, $|\overrightarrow{E _b}|=4|E _c|$



Multiple choice physics electric fields introduction to electrostatic force electric force charging and discharging

Objects with the same type of charges attract each other.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Object with same nature of charges repel each other i.e, positive charges repel positive charge and negative charges repel negative charge.

   And charges with opposite nature attract each other that is negative and positive charge attract each other.

Given statement is $False$.