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Kruka [31]
2 years ago
5

Which of the following is the best thermal insulator?

Physics
2 answers:
Mama L [17]2 years ago
5 0

Answer: A. Air

Explanation: Air is a poor thermal conductor because it's particles are farther apart.

serious [3.7K]2 years ago
3 0

Answer:

A. Air

Explanation:

A thermal insulator is a material that does not let the heat trasmitting through it, or it transmits heat not very efficiently.

Generally, the lower the density of the material, the better insulator the material is: this is because in materials with very low density, particles are very spread apart, so they cannot collide with each other, and so the vibrations of the particles (which determine how hot a substance is) cannot be transmitted very efficiently.

In the options listed in this problem, air is the material with lowest density, therefore it is the best thermal insulator among them.

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2. List a similarity between magnetic force and gravitational force,
DedPeter [7]

Answer:

Both Electrical and Magnetic Forces take place between two charged objects

Explanation:

3 0
2 years ago
A balloon of mass M is floating motionless in the air. A person of mass less than M is on a rope ladder hanging from the balloon
Tasya [4]

Let the mass of the person be m. Total momentum is conserved (because the exterior forces on the system are balanced), especially the component in the vertical direction.

Given that,

Mass of gallon is M

Let man mass be m

Velocity of man is v

Let velocity if ballot be Vb

When the person begin to move we have

Conservation of momentum

mv + MVb=0

MVb=-mv

Vb= -(m/M) v

Given that the mass of man is less than mass of balloon. i.e. m<M

So, if m<M, then, m/M <1

Therefore, .

Vb= -(m/M) v

Vb< -v

This implies that the velocity of balloon is less than the velocity of man and if is also moving in opposite direction

So the man is moving upward, then the balloon is moving downward and it's velocity is less than the velocity of man,

The answer is C

Down with a speed less than v

6 0
3 years ago
Read 2 more answers
A force of 30n is applied to a screwdriver to pry the lid off of a can of paint. The screwdriver applies 75n of force to the lid
gizmo_the_mogwai [7]
The mechanical advantage of the screwdriver that is being described above is equal to 75N. This means that for every 30N that is applied on the screwdriver, this simple machine would in turn apply 75N of force to the lid of the can. 
3 0
2 years ago
An alternator consists of a coil of area A with N turns that rotates in a uniform field B around a diameter perpendicular to the
svet-max [94.6K]

Answer:

(a): emf = \rm 2\pi f NBA\sin(2\pi ft).

(b): Amplitude of alternating voltage = 20.942 Volts.

Explanation:

<u>Given:</u>

  • Area of the coil = A.
  • Number of turns of coil = N.
  • Magnetic field = B
  • Rotation frequency = f.

(a):

The magnetic flux through the coil is given by

\phi = \vec B \cdot \vec A=BA\cos\theta

where,

\vec A = area vector of the coil directed along the normal to the plane of the coil.

\theta = angle between \vec B and \vec A.

Assuming, the direction of magnetic field is along the normal to the plane of the coil initially.

At any time t, the angle which magnetic field makes with the normal to the plane of the coil is 2\pi ft

Therefore, the magnetic flux linked with the coil at any time t is given by

\phi(t) = NBA\cos(2\pi ft)

According to Faraday's law of electromagnetic induction, the emf induced in the coil is given by

e=-\dfrac{d\phi}{dt}\\=-\dfrac{d(NBA\cos(2\pi ft))}{dt}\\=-NBA(-2\pi f\sin(2\pi ft))\\=2\pi f NBA\sin(2\pi ft).

(b):

The amplitude of the alternating voltage is the maximum value of the emf and emf is maximum when \sin(2\pi ft)=1.

Therefore, the amplitude of the alternating voltage is given by

e_o = 2\pi ft NBA.

We have,

N=100\\A=10^{-2}\ m^2\\B=0.1\ T\\f=2000\ rev/ min = 2000\times \dfrac{1}{60}\ rev/sec=33.33\ rev/sec.

Putting all these values,

e_o = 2\pi \times 33.33\times 100\times 0.1\times 10^{-2}=20.942\ Volts.

7 0
3 years ago
A ray in glass arrives at the glass-water interface at an angle of 48° with the normal. The refracted ray, in water, makes a 72°
dimaraw [331]

Answer:

50.4°

Explanation:

Snell's law states:

n₁ sin θ₁ = n₂ sin θ₂

where n is the index of refraction and θ is the angle of incidence (relative to the normal).

When θ₁ = 48°:

n sin 48° = 1.33 sin 72°

n = 1.702

When θ₁ = 37°:

1.702 sin 37° = 1.33 sin θ

θ = 50.4°

3 0
3 years ago
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