# KVPY (Kishore Vaigyanik Protsahan Yojana) Stream SB-SX (Class 12 & 1st Year B.Sc.) Physics: Questions 219 - 222 of 268

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## Question number: 219

MCQ▾

### Question

A solid copper sphere cools at the rate of 3.20 C per minute, when its temperature is 1770 C. Find the rate at which another solid copper sphere of twice the radius lose its temperature at 3770 C, if in both the cases, the room temperature is maintained at 270 C.

### Choices

Choice (4) Response

a.

b.

7.290C min-1

c.

d.

## Question number: 220

MCQ▾

### Question

If the wavelength of photon emitted due to transition of electron from third orbit to first orbit in a hydrogen atom is λ, then the wavelength of photon emitted due to transition of electron from fourth orbit to second orbit will be –

### Choices

Choice (4) Response

a.

b.

c.

d.

## Question number: 221

MCQ▾

### Question

Two masses m1 = 10 kg and m2 = 810 kg are held 2 m apart. At a point P on the line joining them is the gravitational field equal to zero. The gravitational potential at that point is –

### Choices

Choice (4) Response

a.

b.

c.

d.

## Question number: 222

Appeared in Year: 2015

MCQ▾

### Question

A donor atom in a semiconductor has a loosely bound electron. The orbit of this electron is considerably affected by the semiconductor material but behaves in many ways like an electron orbiting a hydrogen nucleus. Given that the electron has an effective mass of 0.07me, (where me is mass of the electron) and the space in which it moves has a permittivity, then the radius of the electron’s lowermost energy orbit will be close to (The Bohr radius of the hydrogen atom is 0.53 Å)

### Choices

Choice (4) Response

a.

10 Å

b.

100 Å

c.

243 Å

d.

0.53 Å

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