Science - 8th Grade

A student builds a device by wrapping wire around an iron nail and connecting the ends of the wire to a battery, as shown.

• bar magnet

• electric motor

• electromagnet

• generator

Answer explanation

The device described is an electromagnet. Wrapping wire around an iron nail and connecting it to a battery creates a magnetic field, turning the nail into a magnet when current flows, which is the defining characteristic of an electromagnet.

Light and sound waves travel at different speeds through different mediums. Which table identifies the medium through which each wave will move fastest?

• Light Wave - liquid, Sound Wave - gas

• Light Wave - solid, Sound Wave - liquid

• Light Wave - gas, Sound Wave - empty space

• Light Wave - empty space, Sound Wave - solid

Answer explanation

Light waves travel fastest in empty space, as they do not require a medium. Sound waves travel fastest in solids due to closer particle arrangement, allowing quicker energy transfer. Thus, the correct choice is Light Wave - empty space, Sound Wave - solid.

A student attaches a rope to a cart and passes the rope through a pulley. The student attaches a mass to the rope, and the cart rolls up the ramp. Which explains why the cart rolls up the ramp after the student attaches the mass?

• The noncontact force of gravity pulls the mass farther from the cart’s gravitational field.

• The contact force of gravity pulls the mass farther from the cart’s gravitational field.

• The noncontact force of gravity pulls the mass down farther into Earth’s gravitational field.

• The contact force of gravity pulls the mass down farther into Earth’s gravitational field.

Answer explanation

The correct choice explains that the noncontact force of gravity pulls the mass down toward Earth, creating tension in the rope that causes the cart to roll up the ramp.

Select the table that shows how the signals will likely look after being copied many times.

• Table A shows how the signals will likely look after being copied many times.

• Table B shows how the signals will likely look after being copied many times.

• Table C shows how the signals will likely look after being copied many times.

• Table D shows how the signals will likely look after being copied many times.

Answer explanation

Table A accurately represents how signals appear after multiple copies, showing the expected patterns and characteristics that emerge from repeated duplication.

In which type of signal (analog or digital) does the copied signal most closely resemble the original signal in both diagrams?

• Analog

• Digital

• Both

• Neither

Answer explanation

The copied digital signal retains the original's discrete values, making it closely resemble the original in both diagrams. In contrast, analog signals can vary continuously, leading to potential distortions.

Refer to the diagrams labeled A and B. The copied analog signal in both diagrams appears to have more _______ compared to the copied digital signal.

• distortion

• clarity

• amplitude

• frequency

Answer explanation

The copied analog signal typically exhibits more distortion than the copied digital signal due to its continuous nature, which is more susceptible to noise and degradation during transmission and reproduction.

Refer to the diagrams labeled A and B. The type of signal that is less affected by copying, based on the appearance of the copied signal, is:

• Analog signal

• Digital signal

• Both signals are equally affected

• Neither signal is affected

Answer explanation

Digital signals maintain their integrity better when copied, as they consist of discrete values (0s and 1s). In contrast, analog signals can degrade and lose quality due to their continuous nature, making digital signals less affected by copying.

Which type of signal retains its quality better after being copied?

• Analog

• Digital

Answer explanation

Digital signals maintain their quality better when copied because they can be reproduced exactly without degradation, unlike analog signals, which lose quality with each copy due to noise and distortion.

Which type of signal retains its quality better after being copied?

• Analog

• Digital

Answer explanation

Digital signals maintain their quality better when copied because they can be reproduced exactly without degradation, unlike analog signals, which lose quality with each copy due to noise and distortion.

What is the distance between the toy car and the wooden block at the start of the experiment?

• 2 meters

• 1 meter

• 3 meters

• 5 meters

Answer explanation

The distance between the toy car and the wooden block at the start of the experiment is specified as 2 meters, making it the correct choice among the options provided.