Electric Charges and Fields Test

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Electric Charges and Fields Test - 29

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Weekly Quiz Competition

Question 1
1 / -0

In the diagram, three point charges (labeled 1, 2 and 3) are shown, along with the electric field around them. Which charge(s) is/are positive?

A
2 only

B
1 and 2

C
1 and 3

D
1, 2 and 3

Solution

The electric field always originate at the positive charge and terminate at the negative charge.
From figure, the electric field lines originate at the points 1 and 3 but ends at point 2.
Thus points 1 and 3 represent positive charge and 2 represents the negative charge.
Question 2
1 / -0

An electron and a proton are both released from rest 1 meter from a large stationary negative charge, considering only the force from the large stationary negative charge on the proton and electron. Which of the following is true?

A
Neither the proton nor the electron will accelerate

B
The initial acceleration of the proton is greater

C
Both the electron and proton have the same non-zero initial acceleration

D
The initial acceleration of the electron is greater

Solution

The magnitude of electric force between electron and proton is given by $$F=\dfrac{1}{4\pi\epsilon_0}\dfrac{e(-e)}{d^2}$$
The force on each of them is equal in magnitude and is attractive.
The acceleration of a species is given by $$a=\dfrac{F}{m}$$
Since the mass of proton is larger, the acceleration of electron is greater.
Question 3
1 / -0

Electric lines of force about a positive point charge are:

A
radially outwards

B
circular clockwise

C
radially inwards

D
parallel straight lines

E
circular anti-clockwise

Solution

Electric lines of force about a positive point charge are always radially outwards.
Question 4
1 / -0

Electric charge is measured in

A
coulombs

B
amperes

C
volts

D
watts

Solution

The standard unit of charge is coulomb (C). Here ampere is the unit of current, volts is the unit of electric potential difference and watts is the unit of power.
Question 5
1 / -0

The charge is negative, then the electric lines of forces are

A
straight lines converging towards the charge

B
concentric circle with charge at the centre

C
Straight lines radiating away from the charge

D
Non of these

Solution

Lines of force originate from a positive charge and terminate to a negative charge. Hence, when the charge is negative, then the electric lines of force are straight lines converging towards the charge.
Question 6
1 / -0

The force acting between two point charges kept at a certain distance is $$5$$N. Now the magnitudes of charges are doubled and distance between them is halved, the force acting between them is _________ N.

A
$$5$$

B
$$20$$

C
$$40$$

D
$$80$$

Solution

According to Coulomb's law, force between two charge particle $$q_{1}$$ and $$q_{2}$$ at a distance r is $$\dfrac{Kq_{1}q_{2}}{r^{2}}$$.
Given, Initial Force = 5N = $$\dfrac{Kq_{1}q_{2}}{r^{2}}$$.
Now, $$Q_{1}$$ = 2$$q_{1}$$ and $$Q_{2}$$ = 2$$q_{2}$$ and R= $$ \dfrac{r}{2} $$. Now , Force = $$\dfrac{KQ_{1}Q_{2}}{R^{2}}$$ = $$\dfrac{ 2\times 2\times K2q_{1}2q_{2}}{r^{2}}$$ = $$ 16\times \dfrac{Kq_{1}q_{2}}{r^{2}}$$ = $$16\times 5N$$ = 80N.
Therefore, D is the correct option.
Question 7
1 / -0

Coulomb's law relates two charges and distance between them describing the electric force as being:

A
proportional to the sum of the charges

B
inversely proportional to the distance between charges

C
proportional to the product of the charges and inversely proportional to the distance

D
proportional to the product of the charges and inversely proportional to the square of the distance

Solution

Coulomb's law can be given by:
$$F = k\cfrac{q_{1} q_{2} }{r^{2}}$$
$$\therefore F \propto \cfrac{1}{r^{2}}$$
Question 8
1 / -0

Electric lines of force about negative point charge are

A
Circular, anticlockwise

B
Circular, clockwise

C
Radial, outward

D
Radial, inward

Solution

Correct Answer: Option (D)
Around a negative charge force converge and moves inside, so it’s radial and inward.
Question 9
1 / -0

The electric field inside a conductor.

A
Must be zero

B
May be non-zero

C
Must be non-zero

D
(a) and (c) are correct

Solution
Question 10
1 / -0

The force between two charges $$2\mu C$$ and $$4\mu C$$ is $$24 N$$, when they are separated by a certain distance in free space. The forces if, $$(a)$$ distance between them is doubled and $$(b)$$ distance is halved are :

A
$$16N, 80N$$

B
$$8N, 72N$$

C
$$6N, 96N$$

D
$$10N, 68N$$

Solution

We know $$F=\dfrac {kq_1q_2}{r^2}=24N$$
a) When $$r$$ is doubled

$$F=\dfrac {kq_1q_2}{(2r)^2}=\dfrac {kq_1q_2}{4r^2}=\dfrac {24}{4}=6N$$

b) When $$r$$ is halved

$$F=\dfrac {kq_1q_2}{\bigg (\dfrac {r}{2}\bigg )^2}=\dfrac {4kq_1q_2}{r^2}=4\times 24=96N$$

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Electric Charges and Fields Test - 29

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Electric Charges and Fields Test - 29

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Question 1

2 only

1 and 2

1 and 3

1, 2 and 3

Solution

Question 2

Neither the proton nor the electron will accelerate

The initial acceleration of the proton is greater

Both the electron and proton have the same non-zero initial acceleration

The initial acceleration of the electron is greater

Solution

Question 3

radially outwards

circular clockwise

radially inwards

parallel straight lines

circular anti-clockwise

Solution

Question 4

coulombs

amperes

volts

watts

Solution

Question 5

straight lines converging towards the charge

concentric circle with charge at the centre

Straight lines radiating away from the charge

Non of these

Solution

Question 6

$$5$$

$$20$$

$$40$$

$$80$$

Solution

Question 7

proportional to the sum of the charges

inversely proportional to the distance between charges

proportional to the product of the charges and inversely proportional to the distance

proportional to the product of the charges and inversely proportional to the square of the distance

Solution

Question 8

Circular, anticlockwise

Circular, clockwise

Radial, outward

Radial, inward

Solution

Question 9

Must be zero

May be non-zero

Must be non-zero

(a) and (c) are correct

Solution

Question 10

$$16N, 80N$$

$$8N, 72N$$

$$6N, 96N$$

$$10N, 68N$$

Solution

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