Tag: electric fields

Questions Related to electric fields

True Or False?
1)A proton repels an electron.
2)An electron repels a proton.

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

  1. False, False

  2. True, True

  3. True, False

  4. False, True.

Show answer
Correct Option: A
Explanation:

The above statement is false. Unlike charges attract each other. A proton attracts an electron.

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

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

  1. Repel, Attract

  2. Attract, Repel

  3. Always attract

  4. Always repel

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Correct Option: A
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.

Like charges ____________  each other and unlike charges ____________ each other :

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

  1. repel, attract

  2. attract, repel

  3. repel, repel

  4. attract, attract

Show answer
Correct Option: A
Explanation:

The like charges repel and unlike charges attract each other, hence option A is correct answer.

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 $Qq/(Q - q)$.

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

  1. True

  2. False

Show answer
Correct Option: A

 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 

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

  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. $\left| {\overrightarrow {{E _B}} } \right|\parallel 8\left| {\overrightarrow {{E _C}} } \right|$

Show answer
Correct Option: C
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, $|\overrightarrow{E _b}|=4|E _c|$



Objects with the same type of charges attract each other.

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

  1. True

  2. False

Show answer
Correct Option: B
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 $False$.

To construct an air filled capacitor which can store $ 12 \mu C $ of charge, What can be the minimum plate area of the capacitor? (Dielectric strength of air is $3\times 10^6 V/m$ )

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

  1. $0.25 m^2$

  2. $0.45 m^2$

  3. $4.5 m^2$

  4. $0.35 m^2$

Show answer
Correct Option: C

A conducting sphere of radius a has charge Q on it. It is enclosed by a neutral conducting concentric concentric spherical shell having inner radius 2a and outer radius 5a. Find electrostatic energy of system.

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

  1. $\dfrac{5}{12} \dfrac{kQ^2}{a}$

  2. $\dfrac{11}{12} \dfrac{kQ^2}{a}$

  3. $]dfrac{kQ^2}{2a}$

  4. $none$

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Correct Option: D

A capacitor is a perfect insulator for:

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

  1. constant direct current

  2. alternating current

  3. direct as well as alternating current

  4. variable direct current.

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Correct Option: C

Four charges $+Q,-Q,+Q$ and $-Q$ are situated at the corners of a square; in a sequence then at the centre of the square:

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

  1. $E=0,V=0$

  2. $E=0,V\neq 0$

  3. $E\neq 0,V=0$

  4. $E\neq 0,V\neq 0$

Show answer
Correct Option: C
Explanation:

Four charges $+Q$, $-Q$, $+Q$, $-Q$.

In this context, $E\neq 0$ but $V=0$ because. $E$ is not cancel out to each other but $V$ is cancel out each other.