The speed of sound is greater in ice (4000 m/s), then in water (1500 m/s), then in air (340 m/s). The explanation for this is the differente state of the matter in the three cases.
In fact, sound waves travel faster in solids (like ice), then in liquids (like water), then in gases (like air). This is because the speed of the sound wave depends on the density of the medium: the greater the density, the faster the sound wave. This can be easily understood by thinking at how a sound wave propagates: a sound wave is a vibration of molecules, which is transmitted throughout the medium by collision of the molecules. Therefore, the smaller the spacing between the molecules (such as in solids), the more efficient is the propagation, and so the sound wave is faster. On the contrary, there is a large spacing between molecules in gases (such as in the air), so there are less collisions between the molecules and so the wave is not transmitted efficiently, and so it has less velocity.
Answer:
A <em>concave</em><em> </em><em>lens</em><em> </em><em>is</em><em> </em><em>thinner</em><em> </em><em>at</em><em> </em><em>the</em><em> </em><em>cen</em><em>ter</em><em> </em><em>and </em><em>thick</em><em>er</em><em> </em><em>at</em><em> </em><em>the</em><em> </em><em>edges</em><em> </em><em>while</em><em> </em><em>a</em><em> </em><em>convex </em><em>lens </em><em>is</em><em> </em><em>thicker</em><em> </em><em>at</em><em> </em><em>the</em><em> </em><em>centre</em><em> </em><em>and</em><em> </em><em>thinner</em><em> </em><em>at</em><em> </em><em>the</em><em> edges</em><em>.</em>
Water evaporates at 100⁰C
So change in temperature = 100-20 = 80⁰C
Amount of water to be evaporated = 1 liter = 1L*1kg/liter = 1 kg
Specific heat of water is 1 calorie/gram ⁰C = 4.186 joule/gram =4186 J/kg
So heat required E = mcΔT = 1 * 4186 *80= 334880 J =334.88 kJ
So amount of heat require to evaporate water = 334.88 kJ
D) Partial charge cannot be removed, because charge is a discrete quantity that may exist only at certain values
Explanation:
The electric charge of an object is a property of the object that is related to the ability of the object to experience/exert an electric force: if the object is electrically charge, then it is attracted or repelled by other electrically charged object.
The electric charge of an object depends on the amount of charged particles it has on it. In particular, the fundamental particles that carry electric charge are:
- Protons: they carry electric charge of +e
- Electrons: they carry electric charge of -e
Where "e" is the fundamental charge (
). Therefore, one proton carry a charge of +e and one electron carry a charge of -e.
An electron is a fundamental particle: this means that it cannot be divided into smaller particles. This also means that it is not possible to remove part of the charge of the electron: in fact, it is said that electric charge exists only as discrete values, being a multiple of 
. Therefore, the correct statement is
D) Partial charge cannot be removed, because charge is a discrete quantity that may exist only at certain values
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They have pure elements or a verity of compounds inside.
