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(b) menarche
The first mensural flow begining at puberty is called menarche.

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(a) 105 Pa
At sea level, the atmospheric pressure is about 105 Pa.

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(a) Increases, increase
The fractional force increases with the increase in roughness of the surface in contact.

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(c) syrinx
Birds produces sound by means of a ring of cartilage called syrinx.

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(a) acidic
Lemon juice is an acidic solution.

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1. The voice box in boys can be seen as the Adam's apple in their throat.
2. The pressure in a liquid at greater depth is greater.
3. Streamlined shape of an object helps reduce friction.
4. The unit used to measure loudness of sound is decibel.
5. The electrode with positive charge is called anode.

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 Column A Column B 1. Cretinism (b) Deficiency of thyroxine 2. Weight (d)  Force 3. Drag (a) Fluid 4. Galton's whistles (e) Training of cats and dogs 5. LED (c) Light emitting diode

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1. True
2. False
Magnetic force is a non-contact force.
3. True
4. False
Sound can travel through solid.
5. True

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1. Force: Newton (N)
2. Pressure: Newton meter-2 (Nm-2)
3. Frequency: Hertz (Hz)
4. Time period: Second (S)
5. Loudness of a sound: Decibel (dB)
6. Current: Ampere (A)

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1. Stringed instruments: Guitar,  Sitar
2. Wind instrument: Flute, Shehnai
3. Percussion instrument: Dholak, Tabla
4. Ghana vadya: Ghatam, Jal tarang
5. Conductors: Copper, Aluminium
6. Insulators: Wood, Plastic

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1. Audible sounds: 20 to 20,000 Hz
2. Human voice: 60 to 13,000 Hz
3. Ultrasonics: Higher than 20,000 Hz
4. Infrasonics: Less than 20 Hz

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Insulin controls the sugar metabolism in the human body. It checks the excess of sugar in the blood.

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According to Pascal's Law, when some pressure is applied on any part of a liquid, an equal and uniform pressure gets transmitted throughout the whole liquid. This means that the pressure applied to a liquid in an enclosed vessel gets transmitted equally across the entire vessel containing the liquid.

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Force of friction is an opposing force that comes into play when a body tries to move over the surface of another body. Surfaces of all the objects have irregularities in the form of minute hills and valleys. These irregularities in the surfaces of interacting objects get interlocked and oppose their relative motion over each other.

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Vibration is a to and fro motion of an object about its mean position.

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According to the principal of gravitational force, all the bodies in the universe attract each other. Gravitational force can be measured by measuring the weight of the bodies involved and the distance between them. It is measured in newtons (N).

Gravitational force = $G\frac{{m}_{1}{m}_{2}}{{r}^{2}}$,
where G is the gravitational constant with a value of 6.67 × 10-11 Nm2/kg2,
m1 and m2 are the masses of two bodies and
r is the distance between the two bodies.

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Factors affecting friction force:

1. Nature of the surface, i.e., the smoothness or roughness of the surface affects the force of friction.

2. The force of friction is directly proportional to the weight of an object.

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Ill effects of noise pollution:

1. It may cause loss of hearing, which can lead to deafness.
2. It causes tension and anger and can interfere with the sleeping pattern of individuals.
3. It causes headache, hypertension and irritability.

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Electrolysis is the process of the decomposition of an electrolyte by passing electric current through it.

Electrolysis could be explained as follows:
1. Two electrodes of a conducting material, such as graphite or iron, are connected to the opposite terminals of a battery and submerged in a solution of the electrolyte.
2. When the battery is switched on, the current starts flowing through the solution and the electrolyte dissociates. Cations start moving toward the cathode (negative electrode) and anions start moving toward the anode (positive electrode). This brings about a chemical change in the solution and the circuit gets completed due to the movement of ions.
3. The flow of current can be tested by connecting a bulb to the circuit. When we switch on the battery, the bulb glows, which proves that current flows through the electrolyte.

Terms involved in electrolysis:

1. Electrolyte: The solution of the chemical, containing cations and anions, in which the electrodes are submerged, is called an electrolyte.
2. Electrodes: The rods of a conducting material that are connected to the terminals of a battery are called electrodes. They conduct electricity through the electrolyte. The positive electrode is called the anode and the negative electrode is called the cathode.

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