# NEET Physics: Questions 1375 - 1379 of 2142

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## Question number: 1375

MCQ▾

### Question

A body initially at 80° C cools to 64° C in 5 minutes and to 52° C in 10 minutes. The temperature of the body after 15 minutes will be

### Choices

Choice (4) Response

a.

42.7° C

b.

47°

c.

40° C

d.

35° C

## Question number: 1376

MCQ▾

### Question

The lengths and radii of two wires of same material are respectively L, 2L, and 2R, R. Equal weights are applied on then. If the elongations produced in them are l 1 and l 2 respectively then their ratio will be

### Choices

Choice (4) Response

a.

4: 1

b.

2: 1

c.

8: 1

d.

1: 8

## Question number: 1377

» Properties of Solids & Liquids » Heat Transfer » Conduction

MCQ▾

### Question

A 5 cm thick ice block is there on the surface of water in a lake. The temperature of air is - 10° C; how much time it will take to double the thickness of the block (L = 80 cal/g, K ice = 0.004 erg/s-k, d ice = 0.92 g cm -3)

### Choices

Choice (4) Response

a.

191 hours

b.

1 hour

c.

1.91 hours

d.

19.1 hours

## Question number: 1378

MCQ▾

### Question

In a photo-emissive cell with exciting wavelength λ, the fastest electron has speed V. If the exciting wavelength is changed to , the speed of the fastest emitted electron will be

### Choices

Choice (4) Response

a.

b.

c.

d.

## Question number: 1379

MCQ▾

### Question

Electrons are accelerated in television tubes through potential difference of about 10 KV

(1) The lowest wavelength of the emitted X-rays is 12.4A

(2) The lowest wavelength of the emitted X-rays is 1.24 A

(3) The highest frequency of the emitted X-rays is 2.4 × 10 8 Hz

(4) The highest frequency of the emitted X-rays is 2.4 × l0 18 Hz

Select the correct answers and mark it according to the following codes:

### Choices

Choice (4) Response

a.

1, 2 and 3 are correct

b.

2 and 4 are correct

c.

1 and 2 are correct

d.

1 and 3 are correct

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