Physics Quiz: Energy And Force

1. Two styrofoam packing beads suspended from threads show a slight repulsion away from each other. from this we can infer that:

Neither bead can be charged

At least one of the beads must be charged

Both beads must be charged and with the same sign charge.

Both beads must be charged and with opposite sign charges.

None of these

The slight repulsion observed between the two styrofoam packing beads suggests that they have the same sign charge. Like charges repel each other, so if the beads are repelling, it indicates that they have the same charge. Since the repulsion is only slight, it suggests that the beads have a relatively low charge. Therefore, the correct answer is that both beads must be charged and with the same sign charge.

Explanation

The slight repulsion observed between the two styrofoam packing beads suggests that they have the same sign charge. Like charges repel each other, so if the beads are repelling, it indicates that they have the same charge. Since the repulsion is only slight, it suggests that the beads have a relatively low charge. Therefore, the correct answer is that both beads must be charged and with the same sign charge.

2. An electric field:

Surrounds a charge

Is said to exist in a region where a net force will act upon a stationary charge

Is where corn and soybeans are grown beneath high voltage transmission lines

Both a and b

None of these

Both options a and b are correct. An electric field surrounds a charge, meaning that it extends outwards from the charge in all directions. Additionally, an electric field is said to exist in a region where a net force will act upon a stationary charge. This means that if a stationary charge is placed in an electric field, it will experience a force due to the presence of the electric field.

Explanation

Both options a and b are correct. An electric field surrounds a charge, meaning that it extends outwards from the charge in all directions. Additionally, an electric field is said to exist in a region where a net force will act upon a stationary charge. This means that if a stationary charge is placed in an electric field, it will experience a force due to the presence of the electric field.

3. A neutral, conducting sphere mounted on an insulting stand. A grounded wire is touched to the sphere. A charged rod is brought near the sphere; the wire is removed and then the rod is removed. the sphere is left with an electrical charge that is:

Neutral

Opposite that of the charged rod

The same as that of the charged rod.

- if the rod was -, but neutral if the rod was +

+ if the rod was + but neutral if the rod was -

When the grounded wire is touched to the conducting sphere, it allows any excess charge on the sphere to flow to the ground, leaving the sphere neutral. When the charged rod is brought near the sphere, it induces a charge on the sphere that is opposite in nature to the charge on the rod. This is due to the principle of electrostatic induction, where the presence of a charged object induces an opposite charge on a nearby conductor. Therefore, when the wire is removed and then the rod is removed, the sphere is left with an electrical charge that is opposite to that of the charged rod.

Explanation

When the grounded wire is touched to the conducting sphere, it allows any excess charge on the sphere to flow to the ground, leaving the sphere neutral. When the charged rod is brought near the sphere, it induces a charge on the sphere that is opposite in nature to the charge on the rod. This is due to the principle of electrostatic induction, where the presence of a charged object induces an opposite charge on a nearby conductor. Therefore, when the wire is removed and then the rod is removed, the sphere is left with an electrical charge that is opposite to that of the charged rod.

4. Consider two point charges that are separated by a distance 2r. If this distance between them is increased to 5r, the force between the charges is:

1/25 as great as it had been

4/25 as great as it had been

1/9 as great as it had been

25 times as great as it had been

None of these

When the distance between two point charges is increased from 2r to 5r, the force between them decreases. According to Coulomb's Law, the force between two charges is inversely proportional to the square of the distance between them. Therefore, if the distance is increased by a factor of 5/2, the force will decrease by a factor of (2/5)^2 = 4/25. Hence, the force between the charges is 4/25 as great as it had been.

Explanation

When the distance between two point charges is increased from 2r to 5r, the force between them decreases. According to Coulomb's Law, the force between two charges is inversely proportional to the square of the distance between them. Therefore, if the distance is increased by a factor of 5/2, the force will decrease by a factor of (2/5)^2 = 4/25. Hence, the force between the charges is 4/25 as great as it had been.

5. Neutral objects such as bits of straw will be:

Weakly attracted by - charged objects

Weakly attracted by + charged objects

Weakly repelled by neutral objects

Both a and b

All correct

Neutral objects such as bits of straw will be weakly attracted by both - charged objects and + charged objects. This is because neutral objects have an equal number of positive and negative charges, so they can be influenced by both types of charges.

Explanation

Neutral objects such as bits of straw will be weakly attracted by both - charged objects and + charged objects. This is because neutral objects have an equal number of positive and negative charges, so they can be influenced by both types of charges.

6. If there is a force of 5.0E-12N acting to the left on an electron, the electric field intensity at the location of this electron will be:

Zero

8.0E-31 n/c to the left

3.1E7 n/c to the left

3.1E7 n/c to the right

None of these

When a force is acting on an electron, the electric field intensity at the location of the electron can be determined using the equation F = qE, where F is the force, q is the charge of the electron, and E is the electric field intensity. In this case, the force acting on the electron is given as 5.0E-12N. Since the charge of an electron is a negative value, the electric field intensity will be in the opposite direction of the force. Therefore, the electric field intensity will be 3.1E7 n/c to the right.

Explanation

When a force is acting on an electron, the electric field intensity at the location of the electron can be determined using the equation F = qE, where F is the force, q is the charge of the electron, and E is the electric field intensity. In this case, the force acting on the electron is given as 5.0E-12N. Since the charge of an electron is a negative value, the electric field intensity will be in the opposite direction of the force. Therefore, the electric field intensity will be 3.1E7 n/c to the right.

7. The molecular chains of the DNA double helix are held together by bonds between adenine and thymine and the other base pair, cytosine, and guanine. What is the force involved if one of these bonds is modeled as an electron 1.8E^-10 m away from a proton?

It is less than 10 - 10 N

7.1E -9 N

4.4 E -6 N

8.0 N

It is more than 10^2 N

The force involved in the bond between adenine and thymine or cytosine and guanine can be calculated using Coulomb's law, which states that the force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. In this case, the bond is modeled as an electron 1.8E^-10 m away from a proton. Since both the electron and proton have charges, there is an electrostatic force between them. The given answer of 7.1E^-9 N indicates that the force involved in the bond is less than 10^-10 N, which suggests a relatively weak force.

Explanation

The force involved in the bond between adenine and thymine or cytosine and guanine can be calculated using Coulomb's law, which states that the force between two charged particles is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. In this case, the bond is modeled as an electron 1.8E^-10 m away from a proton. Since both the electron and proton have charges, there is an electrostatic force between them. The given answer of 7.1E^-9 N indicates that the force involved in the bond is less than 10^-10 N, which suggests a relatively weak force.

8. The arrows below could represent the pattern of an electric field around:

A positive ion at the center

Any "point" charge at the center.

An electron or a negative ion at the center

None of these.

The arrows below represent the pattern of an electric field around a positive ion at the center. Positive ions have a positive charge, and electric field lines always point away from positive charges. Therefore, the arrows would radiate outward from the positive ion, indicating the direction of the electric field.

Explanation

The arrows below represent the pattern of an electric field around a positive ion at the center. Positive ions have a positive charge, and electric field lines always point away from positive charges. Therefore, the arrows would radiate outward from the positive ion, indicating the direction of the electric field.

9. The electric field is zero:

Inside any conductor

Inside any conductor with a static charge

Inside any material, conductor, or insulator with a static charge.

Never

Always

Inside any conductor with a static charge, the electric field is zero because the charges in a conductor are free to move and will redistribute themselves in such a way that the electric field inside the conductor cancels out. This is known as electrostatic equilibrium. The charges will distribute themselves evenly on the surface of the conductor, resulting in no net electric field inside.

Explanation

Inside any conductor with a static charge, the electric field is zero because the charges in a conductor are free to move and will redistribute themselves in such a way that the electric field inside the conductor cancels out. This is known as electrostatic equilibrium. The charges will distribute themselves evenly on the surface of the conductor, resulting in no net electric field inside.

10. Consider a metal statue whose shape is shown below. If there is a static charge upon this object, the electric field intensity will be strongest:

Near the surface near a

Near the surface near b

With a static charge, the electric field intensity will be uniform around a conductor.

It will be strongest near a if the object is charged - and strongest near b if it charged +

It will be strongest near b if the object is charged - and strongest near a if it charged +

The correct answer is "it will be strongest near b if the object is charged - and strongest near a if it charged +". This answer explains that the electric field intensity will be strongest near point b if the object is negatively charged, and strongest near point a if the object is positively charged. This is because opposite charges attract each other, causing the electric field to be strongest near the opposite charged surface.

Explanation

The correct answer is "it will be strongest near b if the object is charged - and strongest near a if it charged +". This answer explains that the electric field intensity will be strongest near point b if the object is negatively charged, and strongest near point a if the object is positively charged. This is because opposite charges attract each other, causing the electric field to be strongest near the opposite charged surface.