Q101: What happens when you bring the north pole of a magnet near the north pole of another magnet?
Answer: They repel each other
💡 Like poles repel and unlike poles attract; this is a basic rule of magnetism.
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Answer: They repel each other
💡 Like poles repel and unlike poles attract; this is a basic rule of magnetism.
Answer: They go out because the circuit is broken
💡 In a series connection the current has only one path, so if one bulb burns out the path is broken and the current stops in the whole circuit, which is why home appliances are connected in parallel.
Answer: 3 amperes
💡 By Ohm's law: current = voltage ÷ resistance = 12 ÷ 4 = 3 amperes.
Answer: The frequency of the vibration (vibrations per second)
💡 The higher the frequency, the higher the pitch of the sound, while the amplitude of the vibration determines its loudness.
Answer: Sound reflected off a distant surface that comes back to us
💡 An echo is sound reflected off a surface such as a mountain or a wall, and we hear it separately from the original sound if the surface is far enough away.
Answer: About 1 kilometer
💡 Light reaches us almost instantly, while sound travels through air at about 340 meters per second, so in 3 seconds it travels about 1,000 meters.
Answer: That light comes from objects to the eye, so we see them
💡 Ibn al-Haytham corrected the old idea that the eye sends out rays, and showed by experiment that light reflects off objects and enters the eye, which is how we see.
Answer: It splits into the colors of the spectrum
💡 White light is a mixture of colors, and each color bends by a different amount in the prism, so the colors separate; Newton proved this with his prism experiments.
Answer: 30 degrees
💡 The law of reflection: the angle of incidence equals the angle of reflection, and both are measured from the line perpendicular to the mirror's surface.
Answer: Refraction of light
💡 Light refracts, or changes direction, when it passes from water to air because its speed is different in each, so the pencil looks broken.
Answer: Convex mirrors
💡 A convex mirror reflects an image of a wider area, but it makes things look smaller and farther away than they are, which is why it carries a warning for the driver.
Answer: 300,000 kilometers per second
💡 The speed of light in a vacuum is about 300,000 kilometers per second, the highest speed known in the universe.
Answer: It changes the direction of the force, so we pull down to raise the load
💡 A single fixed pulley does not reduce the amount of force, but it changes its direction, and pulling down is easier because we can use our body weight.
Answer: Because it reduces the force needed in exchange for a longer distance
💡 An inclined plane is a simple machine that reduces the force needed in exchange for the barrel traveling a longer distance; the work done does not decrease, but we use less force than if we lifted the barrel straight up.
Answer: Chemical → electrical → light and heat
💡 The battery stores chemical energy, which turns into electrical energy in the wires, and then the bulb turns it into light, with some of it turning into heat.
Answer: The joule
💡 The joule is the unit of energy and work, named after the English scientist James Joule, who studied the relationship between heat and work.
Answer: They reach the bottom together
💡 Without air resistance, all objects fall with the same acceleration no matter their mass; astronaut David Scott tested this on the moon in 1971 with a hammer and a feather.
Answer: 100 newtons
💡 The moon's gravity is about one-sixth of Earth's, so the weight becomes about 600 ÷ 6 = 100 newtons, while his mass stays the same.
Answer: 5 m/s²
💡 By Newton's second law, force = mass × acceleration, so acceleration = 10 ÷ 2 = 5 meters per second squared.
Answer: Inertia: their bodies tend to keep moving
💡 Newton's first law (the law of inertia) states that an object stays at rest or in motion unless a force acts on it, so the passengers' bodies keep moving even though the bus has stopped.