How should I read the Kanji 「受」　in the word　「赤外線受発光部」?


Should it be read 「じゅ」 or 「う」 or something else?




受{う} isn't really a thing in Modern Japanese―that's just part of 受{う}ける or
受{う}かる. Most of the time, if the word is 受ける or 受かる, you can tell how to read
the kanji because of the [okurigana](https://en.wikipedia.org/wiki/Okurigana).
And when there are no okurigana, it's usually じゅ instead.

There are a few deverbal examples where the okurigana may not be used, such as
受付{うけつけ} or 受身{うけみ}. With this sort of word, the okurigana aren't really
needed because the word is no longer a verb, and therefore it doesn't inflect
(change form). And if it doesn't change form, the okurigana aren't needed to
indicate the part of the word that changes.

Sometimes when compound verbs are built on 受{う}け, people choose not to write
the け, although it's still pronounced. They may write 受入れる instead of 受け入れる,
or 受渡す instead of 受け渡す, or 受取る instead of 受け取る. Although this is somewhat less
common, the reason is the same as in the deverbal examples above; since 受け
doesn't change form in these compounds, the okurigana aren't really needed.

But those are more or less exceptions. In most cases, if you see 受 in a big
string of kanji with no okurigana, unless you recognize it as part of a word
like 受付 or 受身, you'll be using Sino-Japanese readings (音読み). The Sino-Japanese
reading for 受 is じゅ, and that's the right reading in this case.

For more discussion about the word 受 appears in, please see naruto's answer.




受{う} isn't really a thing in Modern Japanese―that's just part of 受{う}ける or
受{う}かる. Most of the time, if the word is 受ける or 受かる, you can tell how to read
the kanji because of the [okurigana](https://en.wikipedia.org/wiki/Okurigana).
And when there are no okurigana, it's usually じゅ instead.

There are a few deverbal examples where the okurigana may not be used, such as
受付{うけつけ} or 受身{うけみ}. With this sort of word, the okurigana aren't really
needed because the word is no longer a verb, and therefore it doesn't inflect
(change form). And if it doesn't change form, the okurigana aren't needed to
indicate the part of the word that changes.

Sometimes when compound verbs are built on 受{う}け, people choose not to write
the け, although it's still pronounced. They may write 受入れる instead of 受け入れる,
or 受渡す instead of 受け渡す, or 受取る instead of 受け取る. Although this is somewhat less
common, the reason is the same as in the deverbal examples above; since 受け
doesn't change form in these compounds, the okurigana aren't really needed.

But those are more or less exceptions. In most cases, if you see 受 in a big
string of kanji with no okurigana, unless you recognize it as part of a word
like 受付 or 受身, you'll be using Sino-Japanese readings (音読み). The Sino-Japanese
reading for 受 is じゅ, and that's the right reading in this case.

For more discussion about the word 受 appears in, please see naruto's answer.

