Physics Test 55

Result

Physics Test 55

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Weekly Quiz Competition

Question 1
4 / -1

Distance of the centre of mass of a solid uniform cone from its vertex is z₀. If the radius of its base is R and its height is h then z₀ is equal to:

A
5h/8

B
3h²/8R

C
h²/4R

D
3h/4
Question 2
4 / -1

A red LED emits light at 0.1 watt uniformly around it. The amplitude of the electric field of the light at a distance of 1 m from the diode is:

A
5.48 V/m

B
7.75 V/m

C
1.73 V/m

D
2.45 V/m
Question 3
4 / -1

A train is moving on a straight track with speed 20ms⁻¹. It is blowing its whistle at the frequency of 1000 Hz. The percentage change in the frequency heard by a person standing near the track as the train passes him is (speed of sound =320ms⁻¹) close to:

A
18%

B
24%

C
6%

D
12%
Question 4
4 / -1

When 5V potential difference is applied across a wire of length 0.1 m, the drift speed of electrons is 2.5×10⁻⁴ms⁻¹. If the electron density in the wire is 8 × 10²⁸m⁻³, the resistivity of the material is close to:

A
1.6×10⁻⁶Ωm

B
1.6×10⁻⁵Ωm

C
1.6×10⁻⁸Ωm

D
1.6×10⁻⁷Ωm
Question 5
4 / -1

The excess pressure across a soap bubble of radius r is p=4σ / r, where σ is the surface tension of soap solution. What is the excess pressure across an air bubble of the same radius r formed inside a container of soap solution?

A
σ / r

B
2σ / r

C
4σ / r

D
None of these