Science Exercise: Grade 2 Semester 2 (Electricity, Light & Dark)

Explanation
Fireflies are known for their ability to produce light, a process called bioluminescence. They contain special cells in their abdomen that produce light through a chemical reaction. This light is used for various purposes, including attracting mates and warding off predators. Since fireflies emit light, they can be considered a source of light, making the statement true.

Explanation
This statement is false because the current in a battery can flow in both directions - positive and negative. The positive current represents the flow of electrons from the negative terminal to the positive terminal of the battery, while the negative current represents the flow of electrons in the opposite direction. Therefore, a battery can have both positive and negative currents.

Explanation
The statement is false because the number of shadows a person has is directly related to the number of light sources, not the number of light sources they block. Since Syamil blocks 6 light sources, it does not necessarily mean that he will have 3 shadows. The number of shadows depends on the angles at which the light sources are positioned and the position of the person in relation to those light sources.

Explanation
The statement suggests that a buzzer can make things move or spin. However, this is not true. A buzzer is an electronic device that produces a buzzing or beeping sound. It does not have the capability to physically move or spin objects. Therefore, the correct answer is False.

Explanation
An insulator is a material that does not allow the flow of electricity. It has high resistance, which means that it inhibits the movement of electrons. Therefore, electricity cannot pass through an insulator. This makes the statement "An insulator can not be passed by electricity" true.

Explanation
Plastics and woods are actually insulators, not conductors. Conductors are materials that allow the flow of electric current, while insulators prevent or resist the flow of electric current. Plastics and woods have high resistance to the flow of electric current, which makes them insulators.

Explanation
The statement is true because both alarm clocks and radios commonly use buzzers as a sound-producing mechanism. A buzzer is a small device that produces a buzzing or beeping sound when an electrical current is passed through it. In alarm clocks, the buzzer is used to wake up the user at a set time, while in radios, it is used to produce sound for listening to music or broadcasts. Therefore, it can be concluded that alarm clocks and radios do use buzzers.

Explanation
The statement is true because both a fan and a VCD player require a motor to function. A motor is responsible for generating the necessary power and rotation in both devices. In a fan, the motor spins the blades to create airflow, while in a VCD player, the motor spins the disc for playback. Therefore, it can be concluded that both the fan and VCD player utilize a motor in their operation.

Explanation
This statement is false because a circuit can work with both positive and negative currents. In fact, many electronic devices rely on alternating currents that constantly change direction. Therefore, it is not necessary for a circuit to have positive current only in order to function properly.

Explanation
The given statement is true. In order to have a working circuit, all the mentioned elements are required. The battery provides the electrical energy, the wire connects all the components, the switch controls the flow of electricity, the bulb holder holds the bulb in place, and the bulb emits light when the circuit is complete. Therefore, all these elements are necessary for a circuit to function properly.