By inspecting the units, you will be able to tell when the equation is incorrect. (Physics, page 25)
In the above sentence, is the verb "to tell" transitive or intransitive?
By inspecting the units, you will be able to tell when the equation is incorrect . " Tell" is used here in the sense of "perceive" or "know". I think this is best analysed as a fused relative construction where t he underlined element is a noun phrase functioning as direct object of transitive "tell".
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By inspecting the units, you will be able to tell when the equation is incorrect.
I take this as
By inspecting the units, you will be able to see that the equation is incorrect on those occasions when it is incorrect.
intransitive
'tell' is used idiomatically. "you can tell' ~ you know; you recognize
You can tell if it's wrong ~ If it's wrong, you can say so.
You can tell when it's wrong ~ When it's wrong, you can say so.
CJ