Explanation

Question: A powder contains 100mg of a radioactive material that emits α-particles. The half-cycle of the isotope is five days. The mass of isotope that remains after ten days will be?

Answer: The half-life of the isotope is 5 days, which means that every 5 days, half of the remaining material decays. After 10 days, there will be two half-lives:

1. First half-life (5 days): 100mg → 50mg (half of the material decays)
2. Second half-life (next 5 days): 50mg → 25mg (half of theq remaining material decays)

So, after 10 days, 25mg of the original 100mg will remain.

Explanation

The symbol Z represents the proton number.

It is also known as the atomic number, which defines the element.

The symbol A represents the mass number (protons + neutrons).

Explanation

The electrostatic force between two electrons is F Newton, and since protons have the same charge magnitude as electrons (but opposite sign).

The force between two protons at the same distance is also F Newton.

Explanation

The order of speed of sound in different mediums, from fastest to slowest, is:

• Solid (approximately 3000-6000 m/s)
• Liquid (approximately 1000-3000 m/s)
• Gas (approximately 300-400 m/s)

Explanation

Long-sightedness is also known as hyperopia.

It is a vision defect where the image is formed beyond the retina, rather than directly on it.

This occurs when the eyeball is too short or the cornea is too flat, causing light to focus at a point behind the retina.

As a result, close objects appear blurry, while distant objects may remain clear.

Explanation

An echo is caused by the reflection of sound waves off a surface or object.

When sound waves reach a surface, some of the energy is reflected back, creating an echo.

This reflected sound wave then travels back to the listener, arriving later than the original sound, causing the echo effect.

Explanation

The speed of sound in air is affected by two main factors:

1. Temperature: As temperature increases, the speed of sound increases. This is because warmer air is less dense, allowing sound waves to travel faster.
2. Humidity: As humidity increases, the speed of sound decreases slightly. This is because water vapor in the air adds mass to the air molecules, making them slightly heavier and slower.

Explanation

Total internal reflection occurs when a light wave reaches the boundary between a denser medium and a rarer medium.

All of the light is reflected back into the denser medium.

Explanation

Security scanners used at night typically employ infrared (IR) technology to detect heat signatures, allowing for nighttime surveillance.

IR waves have a longer wavelength than visible light, making them ideal for detecting heat radiation from objects or people.

Explanation

When a radioactive nuclide emits a beta (β) particle, it undergoes beta decay.

In beta decay, a neutron in the nucleus is converted into a proton and an electron (the beta particle).

As a result, the atomic number (proton number) of the nucleus increases by 1.