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GRADE 8 PRACTICE

Physics Problems: Charge and electric field, Grade 8

Electrification, atom, law of conservation of charge and field.

27 problems across 6 sub-topics
Practise in the interactive mode

Here the conditions and analysis of the solution can be read without an account. In the simulator, you need to collect the same analyzes yourself: “Given,” formulas, order of steps and answer.

Problem statements

The answer options are there to check against, and the walkthrough opens under each problem.

27 problems
Position in this set: 1 from 27

Problem #28

Charging, conductors and dielectrics

What concept does the description correspond to: “The process by which objects acquire or redistribute electric charge through contact, rubbing or induction.»?

Answer options

  1. \text{Charging}
  2. \text{Two signs of charge}
  3. \text{Conductors and dielectrics}
  4. \text{Capillary action}
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Given
\text{Description}
\text{The process by which objects acquire or redistribute electric charge through contact, rubbing or induction.}
Find

\text{name concepts}

  1. \text{Let's compare approval with definition}

    Electrons can pass between materials when they touch and separate. An initially neutral object gaining extra electrons becomes negative; one losing electrons becomes positive. Two initially neutral objects acquire final charges of equal magnitude and opposite sign if the pair exchanges no charge with the surroundings.

  2. \text{Let's formulate conclusion}\text{Concept} = \text{Charging}

Answer\text{Concept} = \text{Charging}

Position in this set: 2 from 27

Problem #29

Charging, conductors and dielectrics

What concept does the description correspond to: “Like electric charges repel, and opposite charges attract.»?

Answer options

  1. \text{Two signs of charge}
  2. \text{Charging}
  3. \text{Conductors and dielectrics}
  4. \text{Capillary action}
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Given
\text{Description}
\text{Like electric charges repel, and opposite charges attract.}
Find

\text{name concepts}

  1. \text{Let's compare approval with definition}

    Positive and negative signs are conventional, but they describe electric interactions and electron transfer unambiguously.

  2. \text{Let's formulate conclusion}\text{Concept} = \text{Two signs of charge}

Answer\text{Concept} = \text{Two signs of charge}

Position in this set: 3 from 27

Problem #30

Charging

A charged metal sphere was touched by an uncharged metal rod with an insulating handle. What will happen?

Answer options

  1. \text{Part charge will be redistributed by both conductors}
  2. \text{Charge will remain only B point touch}
  3. \text{All electrons will disappear}
  4. \text{Rod not interacts because of pens}
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Given
\text{body}
\text{two conductor}
Find

\text{Distribution charge}

  1. \text{B conductor free carriers can move}
  2. \text{After contact system comes K electrostatic balance}\text{charge distributed}

Answer\text{part charge will pass on rod}

Position in this set: 4 from 27

Problem #31

Atomic structure and charge conservation

What concept does the description correspond to: “An atom consists of a positively charged nucleus and negative electrons. In a neutral atom, total positive and negative charges are equal in magnitude.»?

Answer options

  1. \text{Electrical structure of the atom}
  2. \text{Law of conservation of charge}
  3. \text{Elementary charge}
  4. \text{Capillary action}
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Given
\text{Description}
\text{An atom consists of a positively charged nucleus and negative electrons. In a neutral atom, total positive and negative charges are equal in magnitude.}
Find

\text{name concepts}

  1. \text{Let's compare approval with definition}

    Losing electrons forms a positive ion, gaining extra electrons forms a negative ion.

  2. \text{Let's formulate conclusion}\text{Concept} = \text{Electrical structure of the atom}

Answer\text{Concept} = \text{Electrical structure of the atom}

Position in this set: 5 from 27

Problem #32

Atomic structure and charge conservation

What concept does the description correspond to: “The algebraic sum of the electric charges of a closed system remains constant.»?

Answer options

  1. \text{Law of conservation of charge}
  2. \text{Electrical structure of the atom}
  3. \text{Elementary charge}
  4. \text{Capillary action}
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Given
\text{Description}
\text{The algebraic sum of the electric charges of a closed system remains constant.}
Find

\text{name concepts}

  1. \text{Let's compare approval with definition}

    Charging does not create charge from nothing: electrons pass between objects, conserving total charge.

  2. \text{Let's formulate conclusion}\text{Concept} = \text{Law of conservation of charge}

Answer\text{Concept} = \text{Law of conservation of charge}

Position in this set: 6 from 27

Problem #33

Charge conservation

Two isolated bodies had charges +5 nC and -2 nC, then came into contact. What will be the total charge of the system?

Answer options

  1. +3\,\text{нКл}
  2. -7\,\text{нКл}
  3. +7\,\text{нКл}
  4. 0\,\text{нКл}
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Given
q_1
+5\,\text{нКл}
q_2
-2\,\text{нКл}
Find

q_{\Sigma}

  1. q_{\Sigma}=q_1+q_2q_{\Sigma}=5-2\,\text{нКл}q_{\Sigma} = +3\,\text{нКл}

Answer+3\,\text{нКл}

Position in this set: 7 from 27

Problem #34

Charge interaction and electric field

What concept does the description correspond to: “The interaction force between point charges is proportional to the product of their charge magnitudes and inversely proportional to the square of their separation.»?

Answer options

  1. \text{Coulomb's law}
  2. \text{Electric field}
  3. \text{Static electricity}
  4. \text{Capillary action}
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Given
\text{Description}
\text{The interaction force between point charges is proportional to the product of their charge magnitudes and inversely proportional to the square of their separation.}
Find

\text{name concepts}

  1. \text{Let's compare approval with definition}

    The direction of the force is along the line between the charges; the sign of the charges determines attraction or repulsion.

  2. \text{Let's formulate conclusion}\text{Concept} = \text{Coulomb's law}

Answer\text{Concept} = \text{Coulomb's law}

Position in this set: 8 from 27

Problem #35

Charge interaction and electric field

What concept does the description correspond to: “A form of matter created by electrical charges and exerting a force on other charges.»?

Answer options

  1. \text{Electric field}
  2. \text{Coulomb's law}
  3. \text{Static electricity}
  4. \text{Capillary action}
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Given
\text{Description}
\text{A form of matter created by electrical charges and exerting a force on other charges.}
Find

\text{name concepts}

  1. \text{Let's compare approval with definition}

    Electric field strength gives force per unit positive test charge; field lines are directed from positive to negative.

  2. \text{Let's formulate conclusion}\text{Concept} = \text{Electric field}

Answer\text{Concept} = \text{Electric field}

Position in this set: 9 from 27

Problem #36

Electric field

Charges of 2 µC and 3 µC are in a vacuum at a distance of 0.3 m. Find the magnitude of the force, taking k = 9·10⁹ N m²/C².

Answer options

  1. 0{,}6\,\text{Н}
  2. 0{,}06\,\text{Н}
  3. 1{,}8\,\text{Н}
  4. 6\,\text{Н}
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Given
q_1
2\,\text{мкКл}2\cdot10^{-6}\,\text{Кл}
q_2
3\,\text{мкКл}3\cdot10^{-6}\,\text{Кл}
r
0{,}3\,\text{м}
Find

F

  1. F=k\frac{|q_1q_2|}{r^2}F=9\cdot10^9\frac{2\cdot10^{-6}\cdot3\cdot10^{-6}}{0{,}3^2}\,\text{Н}F = 0{,}6\,\text{Н}

Answer0{,}6\,\text{Н}

Position in this set: 10 from 27

Problem #127

Charging, conductors and dielectrics

B core everyone neutral atom 8 protons. How much total electrons B 3 such atoms?

Answer options

  1. 24\,\text{электронов}
  2. 48\,\text{электронов}
  3. 12\,\text{электронов}
  4. 72\,\text{электронов}
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Given
Z
8\,\text{протонов}
n
3\,\text{атомов}
Find

N

  1. N=ZnN=8 \cdot 3N=24\,\text{электронов}

    In a neutral atom, positive and negative charges cancel out. We multiply the number of electrons of one atom by the number of atoms.

Answer24\,\text{электронов}

Position in this set: 11 from 27

Problem #128

Charging, conductors and dielectrics

B core everyone neutral atom 13 protons. How much total electrons B 4 such atoms?

Answer options

  1. 104\,\text{электронов}
  2. 52\,\text{электронов}
  3. 26\,\text{электронов}
  4. 156\,\text{электронов}
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Given
Z
13\,\text{протонов}
n
4\,\text{атомов}
Find

N

  1. N=ZnN=13 \cdot 4N=52\,\text{электронов}

    In a neutral atom, positive and negative charges cancel out. We multiply the number of electrons of one atom by the number of atoms.

Answer52\,\text{электронов}

Position in this set: 12 from 27

Problem #129

Charging, conductors and dielectrics

Neutral atom with 12 protons lost 2 electrons. How much electrons Remaining B ion?

Answer options

  1. 20\,\text{электронов}
  2. 10\,\text{электронов}
  3. 5\,\text{электронов}
  4. 30\,\text{электронов}
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Given
Z
12\,\text{протонов}
n
2\,\text{электронов}
Find

N

  1. N_0=ZN_0=12N_0=12\,\text{электронов}

    First, we determine the number of electrons of a neutral atom.

  2. N=N_0-nN=12 - 2N=10\,\text{электронов}

    The loss of electrons gives a positive charge.

Answer10\,\text{электронов}

Position in this set: 13 from 27

Problem #130

Charging, conductors and dielectrics

Neutral atom with 13 protons lost 3 electrons. How much electrons Remaining B ion?

Answer options

  1. 20\,\text{электронов}
  2. 5\,\text{электронов}
  3. 10\,\text{электронов}
  4. 30\,\text{электронов}
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Given
Z
13\,\text{протонов}
n
3\,\text{электронов}
Find

N

  1. N_0=ZN_0=13N_0=13\,\text{электронов}

    First, we determine the number of electrons of a neutral atom.

  2. N=N_0-nN=13 - 3N=10\,\text{электронов}

    The loss of electrons gives a positive charge.

Answer10\,\text{электронов}

Position in this set: 14 from 27

Problem #131

Charging, conductors and dielectrics

Two identical metal ball carry charges 12 and 4 nCl. them connected and disconnected, then one ball connected with third like this same uncharged ball. Find charge third ball. System isolated.

Answer options

  1. 8\,\text{нКл}
  2. 2\,\text{нКл}
  3. 4\,\text{нКл}
  4. 12\,\text{нКл}
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Given
q_1
12\,\text{нКл}
q_2
4\,\text{нКл}
Find

b

  1. q=q_1+q_2q=12 + 4q=16\,\text{нКл}

    The full charge of the first two balls is retained.

  2. a=\frac{q}{2}a=\frac{16}{2}a=8\,\text{нКл}

    The charge is divided equally between identical balls.

  3. b=\frac{a+0}{2}b=\frac{8}{2}b=4\,\text{нКл}

    At the second contact, the available charge is again divided equally.

Answer4\,\text{нКл}

Position in this set: 15 from 27

Problem #132

Charging, conductors and dielectrics

Two identical metal ball carry charges 20 and 12 nCl. them connected and disconnected, then one ball connected with third like this same uncharged ball. Find charge third ball. System isolated.

Answer options

  1. 16\,\text{нКл}
  2. 4\,\text{нКл}
  3. 24\,\text{нКл}
  4. 8\,\text{нКл}
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Given
q_1
20\,\text{нКл}
q_2
12\,\text{нКл}
Find

b

  1. q=q_1+q_2q=20 + 12q=32\,\text{нКл}

    The full charge of the first two balls is retained.

  2. a=\frac{q}{2}a=\frac{32}{2}a=16\,\text{нКл}

    The charge is divided equally between identical balls.

  3. b=\frac{a+0}{2}b=\frac{16}{2}b=8\,\text{нКл}

    At the second contact, the available charge is again divided equally.

Answer8\,\text{нКл}

Position in this set: 16 from 27

Problem #133

Atomic structure and charge conservation

B core everyone neutral atom 8 protons. How much total electrons B 3 such atoms?

Answer options

  1. 48\,\text{электронов}
  2. 24\,\text{электронов}
  3. 12\,\text{электронов}
  4. 72\,\text{электронов}
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Given
Z
8\,\text{протонов}
n
3\,\text{атомов}
Find

N

  1. N=ZnN=8 \cdot 3N=24\,\text{электронов}

    In a neutral atom, positive and negative charges cancel out. We multiply the number of electrons of one atom by the number of atoms.

Answer24\,\text{электронов}

Position in this set: 17 from 27

Problem #134

Atomic structure and charge conservation

B core everyone neutral atom 13 protons. How much total electrons B 4 such atoms?

Answer options

  1. 104\,\text{электронов}
  2. 26\,\text{электронов}
  3. 52\,\text{электронов}
  4. 156\,\text{электронов}
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Given
Z
13\,\text{протонов}
n
4\,\text{атомов}
Find

N

  1. N=ZnN=13 \cdot 4N=52\,\text{электронов}

    In a neutral atom, positive and negative charges cancel out. We multiply the number of electrons of one atom by the number of atoms.

Answer52\,\text{электронов}

Position in this set: 18 from 27

Problem #135

Atomic structure and charge conservation

Neutral atom with 12 protons lost 2 electrons. How much electrons Remaining B ion?

Answer options

  1. 20\,\text{электронов}
  2. 5\,\text{электронов}
  3. 10\,\text{электронов}
  4. 30\,\text{электронов}
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Given
Z
12\,\text{протонов}
n
2\,\text{электронов}
Find

N

  1. N_0=ZN_0=12N_0=12\,\text{электронов}

    First, we determine the number of electrons of a neutral atom.

  2. N=N_0-nN=12 - 2N=10\,\text{электронов}

    The loss of electrons gives a positive charge.

Answer10\,\text{электронов}

Position in this set: 19 from 27

Problem #136

Atomic structure and charge conservation

Neutral atom with 13 protons lost 3 electrons. How much electrons Remaining B ion?

Answer options

  1. 20\,\text{электронов}
  2. 5\,\text{электронов}
  3. 30\,\text{электронов}
  4. 10\,\text{электронов}
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Given
Z
13\,\text{протонов}
n
3\,\text{электронов}
Find

N

  1. N_0=ZN_0=13N_0=13\,\text{электронов}

    First, we determine the number of electrons of a neutral atom.

  2. N=N_0-nN=13 - 3N=10\,\text{электронов}

    The loss of electrons gives a positive charge.

Answer10\,\text{электронов}

Position in this set: 20 from 27

Problem #137

Atomic structure and charge conservation

Two identical metal ball carry charges 12 and 4 nCl. them connected and disconnected, then one ball connected with third like this same uncharged ball. Find charge third ball. System isolated.

Answer options

  1. 8\,\text{нКл}
  2. 2\,\text{нКл}
  3. 12\,\text{нКл}
  4. 4\,\text{нКл}
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Given
q_1
12\,\text{нКл}
q_2
4\,\text{нКл}
Find

b

  1. q=q_1+q_2q=12 + 4q=16\,\text{нКл}

    The full charge of the first two balls is retained.

  2. a=\frac{q}{2}a=\frac{16}{2}a=8\,\text{нКл}

    The charge is divided equally between identical balls.

  3. b=\frac{a+0}{2}b=\frac{8}{2}b=4\,\text{нКл}

    At the second contact, the available charge is again divided equally.

Answer4\,\text{нКл}

Position in this set: 21 from 27

Problem #138

Atomic structure and charge conservation

Two identical metal ball carry charges 20 and 12 nCl. them connected and disconnected, then one ball connected with third like this same uncharged ball. Find charge third ball. System isolated.

Answer options

  1. 8\,\text{нКл}
  2. 16\,\text{нКл}
  3. 4\,\text{нКл}
  4. 24\,\text{нКл}
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Given
q_1
20\,\text{нКл}
q_2
12\,\text{нКл}
Find

b

  1. q=q_1+q_2q=20 + 12q=32\,\text{нКл}

    The full charge of the first two balls is retained.

  2. a=\frac{q}{2}a=\frac{32}{2}a=16\,\text{нКл}

    The charge is divided equally between identical balls.

  3. b=\frac{a+0}{2}b=\frac{16}{2}b=8\,\text{нКл}

    At the second contact, the available charge is again divided equally.

Answer8\,\text{нКл}

Position in this set: 22 from 27

Problem #139

Charge interaction and electric field

Per charge 0{,}000002 Cl acts on a uniform field strength 1000 N/Cl. Find the magnitude of the force using the formula F = |q|E.

Answer options

  1. 0{,}004\,\text{Н}
  2. 0{,}001\,\text{Н}
  3. 0{,}002\,\text{Н}
  4. 0{,}006\,\text{Н}
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Given
q
0{,}000002\,\text{Кл}
E
1000\,\text{Н/Кл}
Find

F

  1. F=qEF=0{,}000002 \cdot 1000F=0{,}002\,\text{Н}

    We take the module of positive charge from the condition.

Answer0{,}002\,\text{Н}

Position in this set: 23 from 27

Problem #140

Charge interaction and electric field

Per charge 0{,}000003 Cl acts on a uniform field strength 2000 N/Cl. Find the magnitude of the force using the formula F = |q|E.

Answer options

  1. 0{,}012\,\text{Н}
  2. 0{,}003\,\text{Н}
  3. 0{,}018\,\text{Н}
  4. 0{,}006\,\text{Н}
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Given
q
0{,}000003\,\text{Кл}
E
2000\,\text{Н/Кл}
Find

F

  1. F=qEF=0{,}000003 \cdot 2000F=0{,}006\,\text{Н}

    We take the module of positive charge from the condition.

Answer0{,}006\,\text{Н}

Position in this set: 24 from 27

Problem #141

Charge interaction and electric field

On a positive charge 2 µC force acts 0{,}006 N. Find the field strength in N/C.

Answer options

  1. 6000\,\text{Н/Кл}
  2. 1500\,\text{Н/Кл}
  3. 9000\,\text{Н/Кл}
  4. 3000\,\text{Н/Кл}
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Given
q
2\,\text{мкКл}
F
0{,}006\,\text{Н}
Find

E

  1. Q=q\cdot10^{-6}Q=\frac{2}{1000000}Q=0{,}000002\,\text{Кл}

    A microcoulomb is a millionth of a coulomb.

  2. E=\frac{F}{Q}E=\frac{0{,}006}{0{,}000002}E=3000\,\text{Н/Кл}

    We divide the force by the test charge.

Answer3000\,\text{Н/Кл}

Position in this set: 25 from 27

Problem #142

Charge interaction and electric field

On a positive charge 5 µC force acts 0{,}02 N. Find the field strength in N/C.

Answer options

  1. 4000\,\text{Н/Кл}
  2. 8000\,\text{Н/Кл}
  3. 2000\,\text{Н/Кл}
  4. 12000\,\text{Н/Кл}
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Given
q
5\,\text{мкКл}
F
0{,}02\,\text{Н}
Find

E

  1. Q=q\cdot10^{-6}Q=\frac{5}{1000000}Q=0{,}000005\,\text{Кл}

    A microcoulomb is a millionth of a coulomb.

  2. E=\frac{F}{Q}E=\frac{0{,}02}{0{,}000005}E=4000\,\text{Н/Кл}

    We divide the force by the test charge.

Answer4000\,\text{Н/Кл}

Position in this set: 26 from 27

Problem #143

Charge interaction and electric field

Initially, two point charges interacted with the force 0{,}8 N. The first charge was increased by 2 once, twice 3 times, and the distance increased by 2 times. Find a new strength. Use the relationship F ∝ q₁q₂/r².

Answer options

  1. 1{,}2\,\text{Н}
  2. 2{,}4\,\text{Н}
  3. 0{,}6\,\text{Н}
  4. 3{,}6\,\text{Н}
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Given
F
0{,}8\,\text{Н}
a
2\,\text{раз}
b
3\,\text{раз}
r
2\,\text{раз}
Find

F_{\text{нов}}

  1. k=abk=2 \cdot 3k=6\,\text{раз}

    The product of charges increases by ab times.

  2. d=r^2d=2 \cdot 2d=4\,\text{раз}

    Increasing the distance weakens the force in proportion to the square.

  3. F_{\text{нов}}=F\frac{k}{d}F_{\text{нов}}=\frac{0{,}8 \cdot 6}{4}F_{\text{нов}}=1{,}2\,\text{Н}

    Let's combine both changes.

Answer1{,}2\,\text{Н}

Position in this set: 27 from 27

Problem #144

Charge interaction and electric field

Initially, two point charges interacted with the force 1{,}2 N. The first charge was increased by 3 once, twice 2 times, and the distance increased by 3 times. Find a new strength. Use the relationship F ∝ q₁q₂/r².

Answer options

  1. 1{,}6\,\text{Н}
  2. 0{,}8\,\text{Н}
  3. 0{,}4\,\text{Н}
  4. 2{,}4\,\text{Н}
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Given
F
1{,}2\,\text{Н}
a
3\,\text{раз}
b
2\,\text{раз}
r
3\,\text{раз}
Find

F_{\text{нов}}

  1. k=abk=3 \cdot 2k=6\,\text{раз}

    The product of charges increases by ab times.

  2. d=r^2d=3 \cdot 3d=9\,\text{раз}

    Increasing the distance weakens the force in proportion to the square.

  3. F_{\text{нов}}=F\frac{k}{d}F_{\text{нов}}=\frac{1{,}2 \cdot 6}{9}F_{\text{нов}}=0{,}8\,\text{Н}

    Let's combine both changes.

Answer0{,}8\,\text{Н}

The theory behind these problems

Work through the topic if a problem will not give in.

Charging, conductors and dielectricsTwo signs of charge, the electroscope and charge redistribution.Atomic structure and charge conservationElectrons, ions, charge quantization and charge conservation.Charge interaction and electric fieldCoulomb's law, electric field strength, and uses and hazards of static electricity.

Formulas by topic

Look up symbols and units of measurement in the reference.

Electric chargeq, Q · КлElectric field strengthE · В/м, Н/КлForceF · Н